Dimmer is fine. Problems will occur when too much voltage is fed to an LED. This will cause them to burn out. The PCB should be fine. Also every LED has its own resistor, so multi-colored boards require a different resistor for each switch with a different color. If you want uniform brightness for all your colors, you will need to do the calculations and ensure that your resistors are supplying each LED with the proper voltage they are designed for.
LEDs are (basically) constant voltage devices. They burn out when too much current flows through them.
Multi colored boards require a different resistor for LED's of a different forward voltage drop (Vf). If you look for LEDs online you will see many have the same or similar Vf's. Some LEDs are white and tinted to get the desired colour.
Uniform brightness calculations are somewhat more difficult than that, as you have to look up the datasheet for each different LED, then calculate a resistance value so it outputs the same amount of lm as the others. Then you need to find a resistor close enough to that ideal value that it'll look the same. Since they are different coulours, you can be off by quite a bit and it'll still look good (probably 10-20% or so, depending if you are examining perceived intensity or absolute brightness, since the eyes operate on a logarithmic scale)
Just wanted to clear some stuff up before anyone got the wrong idea.