Beam color is still a ColorSequence whether you’re using a gradient or a single value, so these can’t be edited simultaneously either. If a property’s three dots open a line graph then you’re looking at a NumberSequence; if they open a gradient editor then you’re looking at a ColorSequence.
In either case, they can only be edited separately. Staff mentioned on this old thread why this happens – determining a sensible starting value in the editor is too difficult.