Thresholds for colors in foreground layer

I’m having problems with the color thresholds and numeric values for the foreground layer. I want to set the exact threshold where the value should change color.

Example: I have created a color template with 4 different colors. I want a range 0-20 to be red, 21-40 to be blue and so forth. I know how to make a user generated color lookup table, but I can’t seem to set user-specific values for color ranges. Further, the scalar bar to the right of the map shows numeric values that do not at all correspond to the values on the map.

How do I set these values?