Choose a color format for the work
HEX is a convenient starting point. Modern CSS spaces help when you want clearer control over lightness and hue.
Use HEX or RGB for a straightforward handoff
HEX and RGB describe sRGB channels. Six-digit HEX is opaque; eight-digit HEX adds alpha at the end. RGB can express opacity explicitly. Use a visible background when judging a transparent color.
Use HSL to explore hue relationships
HSL is easy to adjust, but equal lightness values do not look equally light across different hues. A yellow and a blue with the same HSL lightness can have very different text contrast.
Use OKLCH for a tonal system
OKLCH separates perceptual lightness, chroma and hue. Bright, chromatic values may fall outside sRGB. The workspace maps those values for consistent sRGB exports and tells you when it does.
Treat CMYK as a print workflow
The mathematical CMYK estimate is not a print proof. A printer, substrate and color profile affect output. Ask your print provider for its required ICC workflow before approving physical output.