chelu, these are just a few things in the way of proposed improvements, ideas. Take them as you will.
1 ) Scrollbar style. Default scrolbars lookin' tacky.
2 ) Rollover tile highlights (DONE)
3 ) Remove "showing all" and "showing only comments" text, use more minimal buttons instead of links as well -OR- could be one toggle button that changes per state.
4 ) Format artist list into columns (truncate usernames to minimum char count so cols can be standard widths?)
5 ) Live updates, w/o reloads - Auto-update comments/events, even artist list and tile quantities, every minute or so -OR- when something changes only.
6 ) When artist is clicked, show each graphical tile done, along with tile name.
7 ) Precede board events, in comment window, with a relevant icon, indenting them. My concern is better differentiating them from comments, since comments are most likely the higher priority when looking through that comment window list.
8 ) Tile names are great to have now but they still don't really allow you to quickly locate a tile when you only have it's name. Maybe number rows and columns, with little numbers at top/side of each col/row. Furthermore, hex tiles pretty much defy rows and columns. I don't see how a column-row naming convention will work for them. I suggest plain old numbers, ie: 01, 02, 03, etc.
9 ) Add time/date stamps to board events/comments
10 ) Thumbnails on main page are a nice touch but don't seem to help much if not up to date.
11) Imposed themes. Not sure about imposing themes to begin with really. You may've noticed that I completely disregarded the quack ducks pond theme for the first collab. It simply didn't appeal to me. Without doing this one might think that all collabs will just kinda look the same, which is probably not true. I can see the logic in having a theme - something to provide unity for the whole thing. Thinking more about it, I guess I'd like having themes, if I actually liked the theme; if it worked for
me.
Some collabs theme ideas: Aliens/monsters VS. Robots, Vegetables VS. Fruit (cartoon chars at war), Underground, Underwater, Sky.
12 ) Convert links to clickable hyperlinks in chat.
13 ) Gotta remedy those color issues. Top-right of quack quack collab has obvious issues especially where there's blue on both sides of the tile seams in question.
-Great job on everything! You've really proved you're going the distance with this project and it's not some little random pet project born impulsively on the spur of the moment with no motivation behind it to see it through.
-Love how half-typed comments text stays put while clicking around on different tiles, instead of the typing window resetting/deleting what you've typed.
-I don't mind the black masks covering the approved tiles. But here's how using the bg texture would look:
Structured Collab Themes. With this type of collab the physical "structure" or "landscape" of the board is imposed, but only very generally. Only to give direction, or "structure".
Two pics to 'illustrate' the idea here:
#1
Imagine a painting of a simple horizon. A typical landscape. Sky on top, earth on bottom. Now divy it up into sqaures and let random people fill them each in, like we do with Tzigla now. But bind each artist to sticking to content indicative of either sky or earth. Those doing the transitions have freedom to include both, but in a logical way, where in the end the final result maintains a visual separation of sky and earth.
#2
Same thing going on here but there's an added layer of complexity. In the middle of the landscape there's a building, a castle. How in the heck this would pan out is beyond me, at the moment. But I foresee good potential for this idea.
People may be confused at first, but simply show them some visual examples of what expected of them and surely the idea would become clear and they'd jump in.
This concept adds more depth to the whole effort and gives all contributors a common goal of painting the picture. The same structure template could be used over and over and get wildly different results each time.
Tetris Tiles. Odd-shaped tiles using the shapes of tetris blocks. 'Nuff said.

If a board does not specifically say it's pixel art, it's not. Also, I assume that most pixel art boards will have a fixed palette.
Yes, all pixel art collabs should definitely have a pre-defined palette, or color quantity limit.