Why track last spell's color?

[LordofLaw]

As far as I can tell, once you're in a reaction, exactly which color of the two your last spell was no longer matters: If you're already in purple, regardless of if its purple(red) or purple(blue), casting a red or blue spell leaves you in purple, and casting a yellow spell leaves you in no reaction, ready to enter either green or orange. So why track that at all once you're in a reaction? Also, am I wrong or is the line "The last two Alchemist spells you cast determine your Reaction" pretty much wrong? Your reaction depends not just on your last two spells, but also what your reaction was before those two spells.

[Visty]

easier to code most likely