Roblox has a set of colours which have different names such as Very Black etc
This is because it is used in scripting. So roblox does not have what you're talking about
Well there's a plugin that provides more brick colours. (http://www.roblox.com/Too-many-Colors-item?id=149072392)
If you want to add specific colour to your bricks then make a decal of the colour. There's not much of a customisation besides that.