Option to change color for each Tag Index

[florentin89]

Hi. I wish to be able to change the color for each Tag Index ( A - Z ) in cases when for example I don't have any records for letter B, then I want the letter B to have the color grey. But if I have items which start with letter B, then I want the B letter to have the blue color.
Also when I select a Tag Index I want to change the color to a custom color. I wasn't able to find any option for this.
I will attach a mockup (screenshot) below where you can notice that for X letter we don't have any items, and when the Z letter is highlighted we have a different color.

Thanks,
Flo