The Colle is definitely not an aggressive opening in the classical sense. If you like the positions that you get with the Colle, by all means, play it to your heart's content.
The Colle is a very conservative opening because white plays d4 and then really doesn't make any other moves to occupy the center. Playing for theoretical equality as white might be okay if you just want to get a familiar position, but there are other openings that promise white a greater advantage, which is why top level games rarely, if ever, feature the Colle.
System openings like the Colle don't really teach you how to play chess, they teach you how to play the Colle. The reason that the Colle is recommended to beginners is that the ideas and plans are simple, and it works fairly well against any kind of play by black. White does frequently get an attack on black's kingside, which can be decisive if black does not defend accurately.
The biggest downside to the Colle is this: other openings, like e4 e5, will teach you concepts and themes that will apply to all parts of chess. For instance, how to maneuver your knights and bishops in order to improve the position. In the Sicilian (as either color), you can learn how to attack and defend - always useful. The Colle is really limited to learning how to free the dark square bishop and how to stir up an attack on h7. If black is on top of things, the attack will never come to fruition, and black will get a good game after striking with c5.
So my personal opinion if you want to win lots of games: learn the Colle, study all the possible positions, and memorize the moves. If you want to improve your chess, which will lead to more wins down the road, then play main line openings and only play the Colle occasionally for a change of pace.
Some common "system" openings:
- Colle (
- Colle-Zukertort (white plays the Colle with
Bb2 instead of
- Stonewall Attack (
- King's Indian Attack (
Notice that these openings don't try to occupy the center. By not occupying the center, white avoids confrontation until later in the game. This means that white can develop in a known fashion before initiating contact and only then follow the prescribed plans.