To reproduce the error:

require 'ruby2d'

set width: 500, height: 500

Triangle.draw(
	x1: 0, y1: 0, x2: 100, y2: 100, x3: 200, y3: 200,
	color: [
		[1,1,1,1],[1,1,1,1],[1,1,1,1]
	]
)

show

Saved terminal output

gem info says I have 0.10.0 and 0.9.5 installed, but it says 0.10.0 first. I'm not sure what that means. It says 'nothing to update' though, so I think I'm using the latest version.

System info: macOS 11.2.3