Thank you for playing! I've heard a lot recently that the jumps near the beginning are tight (especially in the flowers level). This was something I made easier! I'm glad you got past it regardless.
The blue phosphorus potions emit light and are what make platforms collidable when the light touches them. The black sulphur potions emit shadow and stops light from hitting the platforms - making them passable. I'm not certain what the predictability issue is that you're referring to? It sound's like you assumed that the light forms were collidable when they weren't in light - which is not the case. If light is matter, things in shadow cannot be touched.
Regardless, thank you for your kind feedback. I have ideas for a full game that I may put online in future.