Building an RGB LED Transilluminator?
There are LED's that alreday have the PWM circuitry built in, like the ws2812b. They are available at adafruit and sparkfun in sheets and strips (and controllers are available). The problem with LED's and transilumnation is you need LED's that have the specific wavelength needed for florescence and I'd rather know the wavelengths ahead of time, and the ws2812b does not have the measured spectrum for its LED's listed in the datasheet, so you would have to measure it yourself.
Or you could roll your own with three LED's that you know the spectrum of, if you do this you'll want to use a circuit like this:

Source: https://www.powerelectronictips.com/solenoids-relays-part-1-2/
(you could switch them with a relay either before or after the LED's or a pmos before the resistor.)
Here is some info on spectra for a LED's

Source: http://www.phos-4.com/