First, lets have a look at the white-balance (WB) and see how the colors are changing in different light.
Have you ever had the problem of too much blue or yellow in you´re pictures? If yes, this is the tutorial for you.

The WB control is the setting where you set the color temperature and the present of white content. (The camera are metering 18 present grey)
When you´re out and shooting some nice scenes you should think about what kind of light there is. If you´re standing in the shadows, use the "shade" WB. If you´re inside, maybe There are 8 different WBs in a Canon 350D and thats one for every situation.
Auto:

Tungsten:



Wrong:



The ISO speed setting is very often a smart tool. If you´re out of light in every form, but need fast shutter-speed. You can often rescue a good picture with a higher ISO speed. The lowest ISO speed on Canon 350D is 100. There is also 200, 400, 800 and 1600. When using 1600 you can easily get grainy pictures.

The ISO speed also controls the colors. When using ISO 100 on 350D, I often miss the nice color contrasts. The problems are often solved when using ISO 200, and then you also gets more light.

ISO 100:

ISO 1600:

As you can see, the 1600 is much ligther in the dark areas...