review colours of overlay's legend

1. In case there is a genetic data overlay with different colours for elements provided, and there is no gene mapping added for Genome; the overlay legend displays only one color of the data overlay.
   If mapping is added, two colours are displayed in the legend, and if there is no Genome added at all in configuration there are still two colours in the legend displayed.
   The legend should contain all colors provided in data overlay.

2. Also, if data overlay contains multiple colours, the legend displays one color less than data overlay provides.

Example of my data overlay contains two colours: hg18-test.txt