From Xojo Documentation

Property (As Color )
aWebGraphics.DrawingColor = newColorValue
ColorValue = aWebGraphics.DrawingColor

New in 2020r1

Supported for all project types and targets.

The currently selected color for the WebGraphics object. This color is used by the various drawing methods.

Sample Code

This example draws a red rectangle:

g.DrawingColor = Color.Red
g.FillRectangle(10, 10, 100, 100)