Proposal: Node Backdrop have the color of it own type

Mockup:

What is the benefit:

• Easier to distinguish node type, especially when zoom out
• More aesthetic

Bonus:

• Node backdrop still prioritize custom color
• Node backdrop color field in Theme Editor can be use as a top-layer color with alpha channel: if the alpha set to Zero then Node Backdrop have the color of it own type like in the Mockup, otherwise it have custom unified color.
• For backdrop transparency, maybe add another number field factor in Theme: Node Editor