Pink to purple........hmm you're saying it's the same brand of antifreeze but the colour differs. Could be one of 2 different possibilities as I'm seeing it:
1. If it's a different batch (you didn't say) it could be the manufacturer is using a different chemical composition. Maybe an OAT as opposed to a HOAT composition now.
2nd possibility is various chemicals/minerals in the water leached into the pipes (D/K if your piping system is metal or "plastic") and is now noticeable in the antifreeze upon draining.
All I can think of.