Allow users to modify colors of labels

[kaustubhharapanahalli]

My actions before raising this issue

• Read/searched the docs
• Searched past issues

Expected Behaviour

Enable users to add more colors based on hex value. This gives the control to the users and allows them to represent classes in any fashion they need.

Current Behaviour

Currently, the number of colors users can change is restricted to 24 colors.

Context

Currently the colors that are provided the pallet are all of the same shades and when we want to present any work related to annotations, it makes us stick to the colors provided.
For example:
Let's say I have a class - road and I have drawn the segmentation mask for the same on an image. To represent that it is a road, I'd want to choose a grey color. So when a person looks at the annotation, he can understand what the segmentation mask is trying to represent without having to think much about it. But now, I have to stick to the provided colors.