Quickest way is to use a square as a diamond shape for Photoshop, create super quick. Simply rotate a square for the most basic of vector designs. Go to the rectangle tool and use the layer option top left, draw the square and then transform it using the bounding box of the square by 45 degrees. OK, as a diamond shape it is a little dull, you can fill it with something and perhaps also give it a stroke. Select the rectangle tool again and then go to the fill and stroke at the top of the application and set to green or blue or perhaps a gradient and also add a stroke of 4px etc. You can also apply styles, add designs on top of the artwork, perhaps apply an effect to give it an extra sparkle such as maximum filter and noise
You can also distort the artwork, squeezing it horizontally or vertically. Or perhaps extend the bottom of the artwork so it is not proportional. Select the direct selection tool and then select just the bottom point of the design. Drag the point down and then hold down the shift key to keep the line straight. You can also tweak the colors, the artwork does not need to be a gray gradient, it can be filled with any number of colors.
If you want to add effects etc as well as perhaps other designs on the artwork, probably a good idea to convert it to a smart object via the layer menu and smart objects and convert command and then go to the filter menu and add effects such as the render ones, lens flare and lighting. You can also add all kinds of colorful presets to the artwork as well as going to the layer menu and layer styles and adding bevels and strokes as well as drop shadows and more. You can also use the styles panel to turn your design into a glass effect or metallic art or plastic or something green etc.
Adding styles
You can also use the pen tool to create the artwork. Personally, I always find it easier to use the grid when I am creating anything that I want to be fairly exact so go to the view menu and show grid and then work on the artwork. Goto the pen tool and set the option to layer and then click on the cross section of the cells and place the first at the top, place the side point a little down and a little way across and then go a little further down with the next point and keep it in-line with the top point vertically and then go to the equidistant point for the side point and then click the first point again to close the vector. Once you have your artwork, created either via the rectangle or the pen tool, you can then continue to manipulate it in the same way.
For a hollow effect, select the rectangle tool (and hold the shift key down) and then create a new layer on the art board and then rotate the square (by 45 degrees) using the bounding box. Duplicate the current design by holding down the alt / option key and dragging and reduce the size of the new design again by using the bounding box. Select both of the layers in the layers panel and then go to the layer menu and combine and then subtract front command. Squeeze horizontally the current vector. Select all the points using the direct selection tool and go to the top of the application (middle) and the path operations and use the merge shape components Once you have done this, you can now go to the edit menu and define custom command and create the hollow artwork. Obviously you can vary the size of the second path the vary the size of the hollow vector design. To use the vector, select in the panel and use with the shapes tool. You can repeat this is in different colors and sizes as well as add styles etc.
If you create the artwork as a vector layer then you can add all kinds of styles to the design. Display the styles panel via the window menu and simply select the diamond as well as clicking the style. You can modify the end result of the shadows and gradients etc via the layer menu and layer styles.
You can also define it as a brush and use as a stroke throughout the app so your artwork can be used with the clone as well as art history as well as the smudge or blur effect. Flatten the vector via the layer menu. Instead of just having the basic design, you can also perhaps add in effects such as Gaussian blur or oil paint etc or perhaps use paint strokes on the design such to give it a little more a hand drawn effect, the artwork should definitely be seen as a start point. Go to the edit menu and define brush command. Select a brush tool such as the paint brush tool and apply it. Modify the brush settings (window menu) such as adding color dynamics, spacing, rotation, texture, etc to your stroke.
The design can also be defined as a pattern. Create a new document with transparency as the background. Create the design as described and then draw that design as a layer, set the color etc and then use the rectangular marquee tool to select around the vector (or just use the entire document) and then go to the edit menu and define pattern. You can now use the artwork in pattern overlays in styles as well as a pattern stamp and as a fill with scripts such as random fill as well as a pattern layer. Go to the patterns panel and drag to the document to your art board and then you can double click the entry in the layers panel and modify the angle as well as the scaling etc. Or use in the random fill or symmetry scripts via the edit menu and fill. Set script to on for the pattern option and set the script to random fill or symmetry etc. Select the required preset and then click OK and now set the size, density, color randomization and click OK. If symmetry, check out option 7. You can also combine with effects such as oil paint etc
You can also save the design for future use. Select the vector, add styles etc, add effects etc and then go to the window menu and libraries and then drag your design into the libraries panel into a particular library or create one. Your design then can be used in future projects.
Create a square via the rectangle tool as a layer, rotate via the bounding box by 45 degrees and you have your artwork. You can also interactively round the corners of the design via the corner widgets. You can create all kinds of different rounding especially if you go to the properties panel which can be found in the window menu. Decouple the linked corner settings and then you can enter a value of 0 for one and 20 points for another etc. You can turn it into a regular vector by using a vector and the combine command in the layers menu and the merge components option in the control bar.
With the custom design, you can apply it as a layer as well as a pixel and also as a path. As a path (and this is defined in the top left of the control bar) you can create a path for use with the flame filter. Create a black background via the fill command in the edit menu. Create a new layer and then create the vector artwork, any size and any position. Go to the filter menu and render and flame. Apply using any of the presets in the filter perhaps with advanced tab and randomize option on. Once you have positioned your flame layer, you can flatten the image via the layer menu and then apply oil paint etc and perhaps tweak the artwork with image menu and adjustments and levels etc