Add axes labels and axes color selectors

These selectors allow the user to modify the colors that the 3d and
parallel plots use.

Fixes #134
Change to listen from axes and labels colors

The code now listens to callbacks from the axes labels color and the
axes line colo selectors. This is consistent across both parallel and
three dimensional plots.

Fixes #134
Change color formats for all spectrum objects

All spectrum objects are now hex6 format i. e. all colors are
represented by 6 characters.
Merge pull request #139 from ElDeveloper/issue_134

Add controllers to change the labels and line color