Choosing LED brightness
Given the conditions, you are looking into super-bright RGB LEDs. Are you planning on using a light diffuser/guide or just bare LEDs?
Light diffuser/guide will look cleaner from afar but also block part of the luminous intensity. It's difficult to quantify how much power you'll need to blast into the LEDs to the actual luminous intensity you'll get in those conditions without a bunch of math, it's probably much easier and fun to figure out by experimenting :)

I'll start with taking a look into Adafruit's RGB lightning offering, they do have strips of RGB LEDs (5050) which are pretty neat and may just be fine for your application, they're pretty cheap so you could order one or two to start with.

I've used SK6812 RGB led for a project and they do have a higher luminous intensity at the cost of more power, they're harder to source though.

Or you could go full-on with these: https://www.adafruit.com/product/2530
Be aware that those may need the heatsink mounted if you use them at high-power.