You want a quick and easy Affinity Photo gradient blend, quadrants etc. Create a new layer via the layer menu in Affinity Photo. Go to the edit menu and fill the image with white or black or another color.
Go to the layer menu and new live filter layer and select color and procedural texture to create a live filter layer associated with the current selected layer.
Click the + on the left of the panel to add the first equation and set the value to 0.2*rx + 0.35*ry where rx and ry are the relative layer coordinates and can be moved at any time and this is for the red channel (or cyan if you are working in CMYK), which is very useful when it comes to creating this result.
Copy that formula and then go to the + again and you will add an entry for the green channel this time and change the equation to say 0.3*rx - 0.45*ry and then repeat this with the blue channel by clicking the plus button again and then enter -0.2*rx + 0.8ry and so on.
Go to the blending modes at the bottom of the panel and select difference. Close the panel.
Go to the layers panel and you will see a procedural texture entry, select the square box for the entry (left of the entry) and then right click and select duplicate.
This will create a new live filter layer with the same settings, double click it and edit it and change the formula to say -0.56*rx + 0.23*ry etc for the red channel and so on. Use the rx and ry to re-position the origin and you will see the colors change as you move it back and forth. Close the panel.
Create another duplicate and so on. You can add multiple entries of this and for each of them, change the equations. You will now have a super colorful design across the screen. Please check out the video above for all the steps.
You can also create a very easy variation with the filters menu by using rx*rx instead of rx but it does means that you have to divide the value by something like 100,000 otherwise you will end up with solid colors. You can use this multiple times and vary the parameters such as 0.2, 0.4 etc and also you can combine with the previous applies by using the layer menu and fade command and use opacity and blending modes such as difference and linear burn Youtube video on subject