Also, is there a way to change multiple items within the same frame?
Yes. How are you doing the color change?
If you're new to AE, you should really start here: Getting started with After Effects
Changing white to any color is rather tricky. Could you show us an example still of the image you are trying to change?
Biggest problem, it's hard to change white to anything without doing some kind of overlay.
- Duplicate the footage so you have a copy of the original, roto out the white shirts so they are all on a separate layer, add a colored shape layer over each shirt and change the blend mode to color
- See the first suggestion but put each shirt on a separate layer
- Use CC 14, add a mask over each shirt and track the mask, then apply a color effect like Fill or Hue Saturation and use the Effects Masking tool introduced in CC 14
- If none of these suggestions work then post a screenshot of your footage and explain what is happening in the shot so we can get a better idea of what problems you are facing
- If you have no idea what Effects Masking, Mask Tracking, or roto is let us know or search for these terms in the After Effects Search Help field at the top right corner of the app