How does it get harder?

Well, let's describe every single stage and work up from there. 

First, you have the Red Stage.

The Red Stage is the first stage and the easiest of them all. Roughly 99% of people can pass this one, as long as you try more than once. It consists only of 1 and 2 block jumps, no problem. Every so often it may have to platforms go higher or lower, but as long as you are patient you should be fine. 

Then comes the Orange Stage.

The Orange stage is where most people fail. At this point, about 55% of the people who passed the red stage will ever get to yellow. You have to beat this stage just to be above average. The orange stage introduces 3 and 3.5 block jumps. Usually diagonal, sometimes it elevates and de-elevates the level. You also have to deal with a big spiral, where most people fail.

Now stuff gets real, it's time for the yellow stage.

This is where everyone gets weeded out. Only the best ~20% from that 55% will ever make it to the next level. That means that only 11% of all players who download this will pass. The yellow stage introduces wall jumps and ladder parkour, as well as far-falls and slime block jumps. 4 block jumps are also scattered around. You have to do every single jump perfectly in order to even see the next color. If you're diligent enough, you will probably make it.

The suffering starts now, welcome to the Green Stage.

The green stage is very harsh, as it introduces 3 things. Disappearing blocks, 1 block run-gaps, and "L__" jumps. The hardest being the "L__" jumps. First of all, less than 20% of the surviving 20% will ever make it to the next part. That means less than 2.2% will ever get past the notorious "Green Stage". The disappearing blocks are ruthless and only last 1 second. The single block jumps stretch out really far, and "L__" jumps are a pain to do, as you need to jump around a pillar, and deal with the disappearing blocks. 

If the suffering started at the Green stage, then hell would be the definition of The Blue Stage.

The Blue Stage uses the power of abstract parkour and moving blocks to make your life very difficult. It's also the shortest stage. The moving blocks are the hardest part, while the abstract parkour is very safe, but also very time-consuming and confusing. A few 'L__" jumps are scattered around, but if you passed the green stage then that should be a breeze. Only 50% of the surviving 2.2% will pass this stage. Meaning only 1% of all people who download this world will ever reach Purple.

The Purple Stage bears no mercy. 

The Purple Stage is just about as hard as the blue stage, but it's a heck of a lot longer. It takes the long-jumps from the yellow stage, and turns it up to 11! Since the people who made it this far are probably very good, ~60% of the surviving 1% will make it! About 0.6% of everyone who started will make it to the final stage... the notorious pink color. (Just like in the mobile game ads... cringe.)

onlY 0.01% cAn rEacH pInK ColOR

Ah yes, the  p i n k   s t a g e. A lot more than 0.01% can pass this. If you managed to beat everything else, then I bet you can get past pink. About 95% of the remaining 0.6% should pass. It's literally just the same pink-glass-pane jump over and over again. It has about as much effort put into it as a mobile game does. (I do be milking the mobile game ad jokes.) Anyways that means that only 0.57% of everyone who downloaded this will ever find out the secret of the PINK CUBE.