If your image is that small, you could probably use the “convert a whole image annotation into a cell and generate subcellular objects method.”
Roughly described here, though I think any code is for 0.1.3.
Once you have objects for your Red and White channels, you can convert them into annotations and AND them through the context menu Annotations->Intersect selected annotations.
Or simply create Subcellular detections for the white objects, and classify them by the intensity of red or green within them.
On the other hand, you might find it more straightforward, depending on the number of images, to use the Simple Threshold tool in M5. No guide on this yet, but short version…
Pick a channel
Verify the mask is what you want. Turn the mask on and off using the poorly circled C button.
Now that I have a Tumor object, I can go ahead and make another annotation for my CD8 positive objects.
Selecting both of these annotations through the Annotations tab, and then right clicking on one in the Viewer window, I can then choose the
Annotations->Intersect selected annotations
and get just the CD8 area inside of the Tumor area.
This process can take a moment, just let it struggle.
In the end, the overlapping area as annotations: