Thanks for posting your query.
You have troubling irregular vaginal bleed and it does not resemble natural periods to me.
The change in color of blood makes the thing more suspicious.
You might be having some local lesion which is causing the break through bleeding.
I would strongly advise you to get a hormonal
assay and a ultrasound
whole abdomen and get evaluated by an experienced gynecologist and try to get the exact cause of the trouble.
Hope I have answered your query.
If you have any questions I will be happy to answer.