yellow + blue = black (shadow, makes invisible, temporary)
Have you got alchemy skill lvl 1? Just mix by dragging one potion over the other.
I did it like this: One pyramid at Kroxy's shop, one in my inventory. Then I dropped it, teleported myself back, bought/sold/rested - teleported back again and picked the pyramid up to proceed.
Kiya
With alchemy skill lvl 2 and small empty flasks you can create potions yourself. Do you know how?
About the shadow trick: Use your swirl attack not ON but NEXT to Josie, so you stay invisible.
[color:"yellow"]How to kill her, click here