Hey, here’s an example of how to do this.
Your material doesn’t actually make sense, you can use a vector parameter directly as a color value instead.
Here’s a color picker UMG widget, it’s just 3 regular sliders and a border widget to preview the color. By default sliders go from 0-1, so that works for Value and Saturation, but you’ll have to multiply the Hue sliders value by 360 to get the full range. Then use a HSV to RGB node to make a linear color variable, promote that to a variable, you will use this as the glow color for your material.
The last bit is just setting the color of the border to preview the color.
Next, set up your material. Yours will be different obviously, but just as an example. Make a Vecto Parameter node and call it GlowColor. Multiply it by a scalar value to increase the strength, then multiply it by your mask to mask out non-glow areas.
Then, in your character, or wherever you want to do this, i.e. wherever you are adding your widget to the viewport, do something like this:
The “Cube” would be your mesh. It’s unnecessary to do that on tick, but as a simple example it should get you in the right direction.