add 2 green sockets to this 4 socket armor. i want 6 sockets in total.

nope, doesnt work that way

thought it worked with a 6 socket recipe

6 socket recipe gives you random colors and is not really worth it unless the item is below ilvl to get 6 sockets
otherwise you are better off quality and spamming jewellers orbs to get 6 sockets - but again the colors will be random

either way you are going to get random colors (the base stats of the item do effect colors to an extent - ie: str armour will be more likely to get red sockets, dex - green, int - blue, str/dex - green&red etc etc.
if the colors you are trying to get are common for your base then usually once you get your 6 sockets just chrome until you get the colors you want, beyond that there are some chromatic bench crafts to increase the chances of hitting the colors you need. if you are trying to get lots of "off" colors then you may have to take more expensive routes - but there are also harvest crafts that help to target colors so its much easier than it used to be. also can try your luck with vorici bench slams for white sockets in research safehouses.

handy tool called vorici chrome calculator that you can use to help determine the best method for your desired outcome - however it is slightly outdated with the new harvest crafts and vorici updates so there may be something better at this point that I am not aware of.

based on your question I would assume you are fairly new and you may want to consider using a tabula rasa instead (i - it is a no level requirement 6 linked item with all white sockets (it is pretty cheap to trade for) - it has no stats otherwise - but it is a very powerful starter armor that can take most builds to end game. Once you have more knowledge then you can focus on an appropriate armor upgrade for your character/skills

Well, it does, just it's not worth it.

If its evasion armor and he needs last 2 sockets green, there is pretty high chance he will get it via crafting bench socket spam. It's advanced technique - let's say there is 4 sockets off-color as he needs it, example BBBR and he needs BBBRGG. So in crafting bench you roll 5 sockets. If 5th one is green, you go to next step, if not, you roll back 4 sockets. It deletes just last one socket, 1st four - in our example BBBR - are left as it is. So you roll again 5S -> 4S until desired outcome is. After that you again continue 5S -> 6S same way. Just every 5S -> 6S roll cost 350 jewellers. This technique is mostly used with 4S off-color items. You roll 3S in bench desired color and then spam 3S/4S craft until desired outcome is there.