Dichromate solution should not turn brown - it is probably contaminated. "Rubbing alcohol" can sometime contain colourant, fragrance, aloe vera, and other unfriendly chemicals - read the label very carefully! Be sure to use pure isopropyl alcohol or acetone for carbon work.

I've had dichro/water/alcohol solutions stay "fresh" for several years - no colour change, and as effective as the day they were mixed.

Should you be concerned? As carbon printing can be tricky enough, I'd be inclined to mix fresh chemicals and eliminate the worry