RGB matrix displays?
Based on what you write, it's hard to know any specifics, but let' discuss the basics.

if you have three LEDs, red green and blue, and maximum brightness of all of them is calibrated, so all three will look as white, then you can encode any color using different RGB values. Well, roughly any color- in professional equipment you have those color profiles, etc., which both combine the brightness calibration and define the color space.

Now, if you are going to show somehting on the matrix, you are expected to have an array of pixels, each will have a value of R, G and B, and you will have to find a way to "download" it once in a while to the matrix. If the display has a controller, i believe it will do the scanning, you just have to update it.