Hello, welcome to the forums, and congrats on taking in the 2 Budgies!
This Budgie is a female, and she is in breeding-season...When a female Budgie goes into breeding-season, one of the immediate tip-offs is that their ceres turn from their normal color and smooth texture to a very rough, scaly, thick, crusty cere, and they also turn very dark brown/red. So this is completely normal. When she comes back out of breeding-season her cere will return to normal color and texture.
I would be cautious if the other Budgie is a male and they are housed together, as you may end-up with fertile eggs, which is something that you don't want to have to deal with. Budgies unfortunately lay a ton of eggs, and some females will lay constant eggs all the time, fertile or infertile, and this is extremely bad for their health. If there isn't already both a cuttlebone and a mineral block inside of her cage, you need to get both for her ASAP, as she needs the Calcium, along with the other vitamins and minerals they provide.
If they came from a "questionable" home, then you don't know how many times they have been bred, possibly over and over and over again...And depending on how old she is, laying clutch after clutch of eggs is really not good...forgetting that you don't want to deal with babies..There are ways that you can sterilize any fertile eggs she may lay, like putting them in the freezer overnight or boiling them for 30 minutes, then putting them back in her nest until she gets bored because she realizes they aren't going to hatch, then you can take them out and throw them away. This keeps her from continually laying more eggs to replace the ones you remove (if you were to just throw them out)....Also, making sure that they wake-up with the sunrise and go to bed with the sunset, and are in a place that they can see these light changes through a window will help to knock her out of breeding-season and also help to tame both of their hormones..
I recently adopted two 1-year-old budgies who weren't in the best of homes previously. I have had budgies before, but haven't seen the brown colour/textured cere that one has. Can you please tell me if this is something to be concerned about? Diet wise they are on pellets, fresh fruit and veg and a mix of cooked grains and some seeds. Thank you! 
