On Barracuda Studios decal sheet "BC32144 Erla Bf 109G-10 - Part 1" we've included a II./JG52 aircraft marked "Black 22". There is some doubt about the color of the numerals though as they look a bit paler than one would expect from black numerals. This could be explained by a glossy black paint used for the numerals or even a glossy fuselage that combined with a low setting sun reflects the light in such a way that creates this pale effect.
Turning to documental evidence, more precisely the losslist of II./JG52, it is clear that normally II./JG52 used White, Black and Yellow numerals. There's also a single mention of red, "Red 2", a WNF built Bf109G-10 that was lost on March 15:th 1945. A photo of a WNF built Bf109G-10 marked with what is likely a red "2" exists and shows that the red was used without outline. So based only on the losslist, Black 22 would seem like the most likelt candidate for the markings.
Another possibility comes from the fact that here was an 8./JG52 formed as part of II./JG52 for at least a month in early 1945. In other words it's likely that at least for a while, a fourth staffel color was used within II./JG52. Given the relative dark tone of the numeral on "22" I believe it's safe to rule out RLM 25 but RLM 24 could be an option. The problem is that not a single loss for an 8./JG52 aircraft can be found in the losslist, but there are also several losses that are simply noted as "II./JG52" without mention of neither Staffel number nor tactical number or color. So while the losslist doesn't prove the existance of blue numerals it can't be used to rule them out either.
If the aircraft was marked Blue 22 due to it being part of 8./JG52 it would have been flown by another staffel of II./JG52 during the spring of 1945 as by the time the yellow rudder and band around the nose were applied, 8./JG52 was already disbanded.
That's all that is know at the moment. Hopefully something will emerge in the future to shed light on this little mystery but for now, this is it. We supplied the option, above is the explanation, the decision is off course yours and yours alone. Have fun!