I just looked at mine and my pixels are messed up too. I can't imagine it being because it is incomplete as the pixels are that of primary colours.

the mushrooms which show up around the tree aren't (most of the time not) visisble only few sparks and when you drop a kid on it it picks up a mushroom.

I thought it was like that because the mushrooms were growing in the deep, dark crevices in the roots of the tree.

Same here

that can it be too, but sometimes i see the bottom and not the top of the mushroom Maybe it is just the tree standing in the way

Did you watch to make sure that your villager was actually succeeding at the construction tasks? Did scaffolding ever appear on the piers? Could you post a screen shot of your piers now? If you don't know how to do that, you can see procedures in this post.

Hi LadyCFII, thank you for your quick response. Yes, scaffolding was there. Tiko was walking from piers to pile of wood then back again to piers.. He became trainee builder on those piers.. Here's screen shot of piers now:

Shakle, completing the piers puzzle is a two part process.