While I was making dye samples with leftover blue food coloring (made with red cabbage and baking soda) I noticed that the dye solution changes dramatically its color in 4 days.
The dye solution you see in the picture above is tap water mixed with some homemade blue food coloring. On day 1 it’s beautiful blue, on day 2 the blue turned to bluish dark green, on day 3 it’s pale olive-green and on day 4 it’s just light beige.
The same effect I noticed in my red cabbage dye samples: fresh red cabbage dye solution seams to dye more blue, while older dye solution dyes the fabric more green. Also, if the fabric is left in the dye for a short time it’s blue, if it’s left in the dye for some hours it’s green, and if the fabric is left in the dye overnight it’s just an ugly pale beige stain.