RangeControl: add solid color to left side of track

[davewhitley]

Is your feature request related to a problem? Please describe.
The current range slider design is not ideal, because it can be difficult to see where the thumb is at a glance. The component is also limited because in the future you may need to have 2 thumbs and adjust the min and max range.

Describe the solution you'd like
The left side of the track should be colored.

Better yet, it should be colored blue to distinguish itself from a disabled state in the future (not sure if there is a disabled state currently).

[paaljoachim]

I just checked and the left side of the Columns slider has a blue color.
I believe we can close this issue. If that is a mistake then please reopen.