Nick Colors lets you pin a specific color to a nickname. Without an override, RetroHexChat derives a color from the nickname itself, so the same person always looks the same — an override wins whenever you want a particular person to stand out.
Assigning a Color
Choose Add, type the nickname, and pick a swatch from the 16-color IRC palette. Select an existing row and choose Edit to change its color, or Remove to fall back to the automatic color.
Opening
Go to Tools > Nick Colors, or right-click a nickname and choose Set Nick Color.