? Selecting 2 of 3 RGB channels in to adjust in Levels

Question

This is a CS4 question (and let me express my ingratitude to Adobe for dropping support for an $1800 set of apps).
In Photoshop CS4, using a G5 (non-Intel), in the Channels view panel (alongside Layers, etc), when it is displaying RGB, Red, Green,and Blue I am able to shift-click, on say, the Red and Blue channels to sleect only those two. The image still displays in full RGB. When I issue command-L (Levels) I end up with the basic Levels disalog box, and instead of it choosing by default "RGB" for adjusting, I now have "RB" and I can adjust Red and Blue together with the sliders, avoiding the green channel. I can do this in, obviously, three combinations.
For some reason, when I try this same thing on a friend's Intel Mac with Photoshop CS4 (same!), shift-clicking the Red and Blue channels in the Channels palette chooses them but the image display now displays without the Green channel influencing the image, thus rendering it unusable for adjusting two channels at once.
I figure that since I am using the same App version on each Mac, maybe there is a setting somewhere I cannot find, or I am forgetting a step on the way to my friend's computer.
Q: How do I choose 2 channels in the Channels palette while still having my image display in full color, and also be able to choose those two channels for adjustment in the Levels?
For those of you who are wondering WHY I would want to adjust 2 channels at once, here's an example: an image looks lsightly too yellow, bt ther eis no yellow channel. Yellow is full Red & Green, so, using my method, I can choose both those channels, and reduce the yellow by reduing R and G together.

Answer 1

You should be able to shift click the red and blue channels, then make the rgb composite visible (make the EYE visible by clicking in that box)