Single Color Square Display

I need a display
It should be square and small like 3x3cm or 5x5cm or everything in between
It should be easy to control with an Arduino even when there are a lot of them
It will be okay even if it can display one color at the time
It should be able to display color like Brown, Grey, Red and Blue.

Please answer, I need it for an exam at school. :frowning:

Use a single RGB led with a diffuser infront (like Neopixels)

// Per.

An RGB (Red, Green, Blue) LED will work OK. Different colours are simply a mix of different brightness of each of those three colours.

Bear in mind that grey is simply "dim white", and brown is a "dim orange".

Look at a colour wheel and you will understand.