Coloring relaxed hair has been a big dilemma in the hair community for quit some time. The thing is, when coloring relaxed hair, the hair has been so compromised with the dual chemical processing that it breaks. Understanding the hair’s elasticity and tensile strength is very important when coloring relaxed hair.
First, a proper hair analysis is required . Only strong durable textures are good candidates. Some people can’t do it depending on texture type and elasticity
The key is to not relax the hair all the way bone straight. Leave some curl and leave room for the lightening process. If you didn't know, hair color will straighten the hair about 30%. Also, remember that the hair that has been opened up by the relaxer and will process 30%-50% faster than hair that’s left natural
When considering what kind of relaxer to use, I recommend one that has 1.75% of sodium Hydroxide or lower. This usually consists of your low lye or mild relaxer systems depending on your texture and density. It's okay for the hair color to color hair that's relaxed that same day. However, in other cases where the hair is finer and less dense, it's better to color hair that's been relaxed 4 days to two weeks prior . Determining what level of lift you should go with, is also something to consider. Hair that has no curl left after the relaxer process can only go up to a level 7 or 8 on the same day. Hair that has retained some curl (elasticity) after being relaxed can go maybe a level higher , but you need to check the elasticity of the hair throughout the whole process .
A bond builder (Olaplex, Wellaplex, etc) will need to be used in the color along with a protein strengthening conditioner.