In case you didn't know the receivers are made from cast aluminum
So let's say your receiver's original finish is not looking so good
What are your options? As noted above the factory receivers are aluminum which means you cannot blue, parkerize or color case harden them, but there are still plenty of options.
You could always sand blast it and leave it in the bare aluminum or....
use sandpaper (600 grit) to get a matte finish
or give it a semi-polished look
......a high polish finish like these folks have done
Here is the one I did on my target rifle project
After polishing you could jewel the entire receiver
You could also chrome plate the receiver
This one is polished, but it sure looks like chrome plating
for that matter you could plate in it nickel, brass or copper as well.
Some people chose to use spray paint, not a bad option as the receiver is mostly protected by the stock
This guy went with a camo theme
Cerakote and Duracoat are also very popular
The one below is from Brimstone Gunsmithing
The one below is from Monarch Defense
These next two were painted with automotive paint, they turned out very nice, the first one almost looks like a high polished blued finish
Powder coating is an option, this is what the factory currently applies to the receivers
Anodizing is another option, although I have seen few factory receivers re-anodized, it can be done. I found these for sale on Armslist
Many aftermarket companies offer their replacement receivers in a multitude of colors, if doing it custom like those above, your color choices are almost limitless
Another anodizing option is the hard coat anodizing like found on AR rifles, this is how some aftermarket receivers are coated, this one is from Brownells
One last option is hydro dipping, there are a ton of different patterns and colors, this one is made to look like carbon fiber, see it here