I find the default text highlight colors too muted — typically I want to highlight something to make sure people notice and choose a bright "highlighter yellow."
However, I have to keep updating the hex every time. I wish that the text editor would save my custom colors in the drop down (as Google docs does).
I'd also love to save custom options for highlight colors, or at least have a dedicated highlight color palette. As-is, the highlights share the same color options as text colors. Only a few colors in this palette are actually usable as highlights which I find limiting.