Ok, just looked in-game. You are talking about modifying armours/weapons right?...Forget everything I just posted as that is for crafting from scratch! Green means you are increasing a stat, red means you are making it worse, Orange means you are adding a stat, grey means no change.
I think The orange square before means you are adding a stat, a green arrow means you are increasing one. For example, if an item had +5 constitution and you add an enhancement that gives you another +5, it will be a green arrow with +10. If your enhancement has +5 strength instead, it will be an orange square with +5 strength. Grey is stuff that is not changing.
I didn't pay much attention to it because you don't really need to tbh...this gives you +10 strength...strength is good!