34, on lowogestrol last 4 years. period length is consistent, but my period was more brown throughout (rusty at beginning) before, and for a year or so has become more red at beginning, a little heavier, while ending with brown.why would this change?

Things just change: The color of menstrual blood can vary from bright red, to dark red, to brown. There is no real significance to the color. If you are saturating more than 1 super tampon per hour or maximum absorbency pad per hour for more than 2 hours, or if you are passing clots bigger than 2.5 cm (the size of a us quarter) then see your doctor.