My first thought was. OMG how boring. However In the end I rather enjoyed it, I especialy liked the way of upgrading guns, Overall, a good stress release game, very simple and repataive,, but fun. :)
If I understood correctly, if the monsters hue is the same as the gems hue, it does no damage, or reduced damage, and I suppose the opposite might apply, the further away the hue, the damage might be greater
I completed level 78 second try. (I was level 76) But even so, if you place the towers with maximum pathing, and have the right skills, It isn't that hard
If you seek to do the impossible: My advice is to do it in small chunks, if you value your sanity at least *gibbers madly as he is lifted into a van in a straight jacket*