Make schedule text readable on light color rooms

[timreyn]

For CubingUSANationals2023, we'd like to have one stage color be yellow. But because the calendar view uses white text, it's pretty unreadable on a yellow background.

Either the "chroma" gem (https://github.com/jfairbank/chroma#other-methods) or "chroma.ts" in typescript (https://github.com/NaridaL/chroma.ts#colortextcolor-color-src) should distinguish between light and dark colors, and use black or white text accordingly.