Here is a good reference list of the pre-defined HTML colors: https://developer.mozilla.org/en-US/docs/Web/CSS/named-colorWithin an equation context, KateX supports colored equation text and backgrounds with the \textcolor{color}{text} and \colorbox{color}{content} functions.this+equation/is=tomato\textcolor{tomato}{this + equation / is = tomato}this+equation/is=tomato Surrounded by a box. Enter math-mode with dollar signs like+this\fcolorbox{aqua}{cadetblue}{Surrounded by a box. Enter math-mode with dollar signs $like + this$}Surrounded by a box. Enter math-mode with dollar signs like+this