This game provides a nice contrast to Aliens Must Die, since it also takes an old idea, but it adds enough new and interesting features to make it a joy to play again. Like Filler, it's very much like JezzBall and Barrack. In fact, it's much more like those games than Filler, and...what's that? I never actually explained what JezzBall and Barrack are? Well, let's start there.
So, JezzBall is an old Windows game. You have a playfield with a bunch of balls bouncing across it, and your cursor controls a gun which can shoot lines either horizontally or vertically. When you click your button, two lines start from your cursor's present position outwards. If a ball happens to hit your lines while they're still moving, then they're destroyed and you lose a life. If both your lines reach the wall safely, then your line becomes solid. If the space on either side of your line is empty, it gets filled in. If both sides still have balls, then your line is at least still useful as a closer wall for future lines. Your goal is to fill up a given percentage of the playfield. Barrack is a classic Ambrosia game for the Mac, with the same basic concept but a few additional twists.
Anyway, colorfill is basically the same formula as described above, with a few twists. First of all, instead of only balls (which are actually colorful triangles), there are two other kinds of enemies: gears which roll along the walls, and long-tailed snakelike objects, both of which have uncanny talents for reaching your line just as it's about to complete. Also, the playing field is not necessarily rectangular. Second, as the name might imply, your lines are brightly colored in a variety of hues; your cursor changes color after every successful shot. This might not seem like a substantial gameplay difference, but the third difference makes it important. In JezzBall, as I mentioned, the empty half of space created by your line (if there is an empty half) is filled. It is thus possible (but very difficult, of course) with a well-timed shot to fill up a very large percentage of space with one shot. In colorfill, however, it's always the smaller half of the two halves created by your line which is filled. This means that, unlike JezzBall, where balls can never be killed, only hemmed into ever-smaller regions, you can destroy enemy objects by trapping them. But wait, there's a catch! If you happen to destroy an enemy object of the same color as your current fill color, two new ones will spawn in your empty space! This can prove particularly challenging when two objects of the same color as your cursor simply insist on staying on opposite sides of the screen.
Anyway, the level design is solid -- there's enough nooks even in the more difficult levels to give you a fighting chance, and overall the game is difficult but not too difficult. The game gets many positive points for not making you replay from the beginning when you die, but allowing you to pick up where you left off. The graphics are, as mentioned earlier, brightly colored and pretty. The music is terrific -- it's bouncy, fun, and truly enjoyable to listen to.
Overall, this is a tremendously entertaining game. It shouldn't take you too long to complete the 21 basic levels, but the 3 bonus levels (where your line moves more slowly) are quite difficult. I also approve of having a badge for doing the wrong thing (intentionally duplicating shapes), which adds a cute little wrinkle.