• 2D
  • How to change the corner radius of a color-rect?

I do not think so, not with a ColorRect node. You can use a Panel node with a custom flat-style panel texture, set the color to white and the corner radius to what you want, and then use self_modulate to change/tint the panel to whatever color you need.

7 months later

@TwistedTwigleg you're right, using a Panel is exactly what I needed!