A few options.
Use heaps of RGB LEDs, wire them in a matrix, add a good handful of shift registers and multiplex the whole shebang. Probably cheapest, but also definitely the hardest.
Use a lot of individually addressable LEDs such as the popular WS2812B ones.
Use a ready made LCD display of appropriate size.
In all cases, depending on how elaborate you want to animate the thing, you probably have to look into more capable hardware such as the Teensy, ESP32 or even RPi. A common ATmega328 based Arduino won't do.