For anyone looking at this now and needing help, This is what worked for me when I stained my white acrylic bath with pink clothes dye (which leaked from a scarf I'd left to soak).

*Put in plug.
*Threw half a pot of baking powder on the stained area.
*Half a bottle of lemon juice.
*Left for 10 secs
*Scrubbed with a typical kitchen sponge (with the green soft scourer - do not use anything too scratchy).
*added water and scrubbed again.
*drained and rinsed (much better but still pink)
*repeated the baking powder and lemon juice
*filled water to cover the stained area and scrubbed more.
*left for 2-3 hours
*scrubbed with the water still in
*drained and rinsed (tiny bit pink)
*Bathroom bleach spray, scrub, rinse.
*99% back to normal!
*Phew!