Not exactly sure of your question. If you need to color match, you'll have to work with the vendor to get them done up right. If I remember correctly, you can send them a part to match and they will color match it and send it back to you along with the paint.
However I think most people assume you won't get a GOOD color match, and just redo the whole rifle.
HK semi-gloss black is a VERY good general-purpose black. Matte black is MATTE and tends to look a little more "washed out" for lack of a better description. Don't let "semi-gloss" fool you... it isn't "shiny" at all and perfectly appropriate for a combat rifle.
I have had good results when mixing about half-and-half HK semi gloss and matte but I'm not sure it is worth the effort to do all the mixing.
Not sure if Lauer has a FAL color in their listing? May be worth a look.