The current picker that shows when using the colour input in Firefox Mobile on Android is not solving any real use cases. It provides a list of 10 hard coded colours (9 + the current value. With no way for the user to customise.
Android unfortunately doesn't provide a system colour picker to use (unlike every other OS), so it'll need to be a custom UI component. Something that lets you choose an R G and B value or even just type in a hex code would be a massive improvement even if a more complex graphical UI would take too many resources.
This is especially needed now that HTML colour inputs can be opted into supporting an alpha value (where an additional slider or opacity would be needed).