JustGeek made a sample set of PCBs to help in color and thickness selection:
There are also functional reasons. A white board could make the reflection from a mounted LED more color neutral, while a black board mounted in a translucent acrylic enclosure would be barely noticeable from the outside.
Similar to the different colors, PCBs also come in varying thicknesses. A thinner board is lighter while a thicker board is more robust. Sometimes the necessary thickness is determined by other factors, but often you can choose from a range of options.
To help me select a nice color and appropriate thickness, I’ve made a set of PCB samples in seven different colors (white, yellow, blue, green, purple, red, black), six different thicknesses (0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.6 mm, 2.0 mm) and two different surface finishes (HASL, ENIG).
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