Imagine this, as a beautician--you are doing your clients brows and following protocol as usual, then all of a sudden, instead of the beautiful warm blonde or cool dark brown tone you are applying, you suddenly see a Hulk inspired green tone turn up on your clients brows and the horror within it begins to emerge.
First of all, take a breath and don't panic! Sometimes it isn't your fault at all! But there a few things you can watch out for in order to best avoid this situation so your client doesn't freak out!
Here are some tips and suggestions to follow:
Always ensure your henna tint is fresh, check the expiration dates at all times and ensure that you keep it for only the amount of months listed on the bottles.
Be aware of your clients skin type and chemistry in combination with dye or tint. Sometimes its not so easy to tell, but at times some clients have had their brows previously dyed with an alternate product and their skin reacts differently to certain chemicals. This could in fact emerge in a different tint than intended.
Most important of all, one key tip that could turn the hairs green is if you don't SET your henna prior to continuing to apply layers. What this means is, once you mix the henna with the developer, wait a few minutes for the consistency to be correct. THEN, after applying your first initial layer, WAIT a minute or two for that to set into the skin and hairs prior to continuing with your second or third layer. This is a key element in the colour turning, you must allow the chemicals to set in so that it tints correctly and evenly.
Also important to know, in many cases, especially with lighter or warmer tones such as Blonde or Golden Brown, if the colour does appear to be greenish--it will go away in a few hours. This is just the skin chemistry and once the henna does oxidize entirely, it settles in more.