color layers is simply color layers
Probably because you work in Grayscale mode. Go to Image > Mode and click RGB Color.
You mean Color Mode? Changing how Photoshop treats and displays colors in an image.
To change color mode go to Image > Mode > choose. To change color profile go to Edit >Color Settings, Edit > Assign Profile or Edit > Convert to Profile.
Lab color spaces is closest to human vision. So, possible answer on your question can be: Lab color space simulates colors closest to human vision.
Color mode is color space you are working in, determines which colors u can use and number of possible colors. RGB is suitable for screens, and by the way use this color mode for your work inside Photoshop.
You can save Lab images in PSD, PSB, Photoshop EPS, Photoshop PDF, Photoshop Raw, TIFF, Photoshop DCS 1.0, and Photoshop DCS 2.0 formats.
RGB is color mode suitable for on screen viewing, rgb layer means that layer is in rgb color space. IN Photoshop you can see (or change) in which color mode you are working from Image > Mode
8 bit what you can see and control in New dialog (File > New), somewhere in the middle of dialog search for Color Mode: - you can change mode from drop down list and next to color mode options is drop down list with bit dept options.
RGB, CMYK, Grayscale, Lab, Indexed color are color modes in Photoshop. What you want to ask? Why we use color modes? To manage colors in image based on image purpose.
What is colour channel in photoshop?
Probably bacause another image is in Grayscale Mode. Image you try to drag and drop must much Color Mode of another image so it is converted on the fly to Grayscale (Black and White). To change Color Mode go to Image > Mode > choose RGB.
Levels in Photoshop are color and brightness correction.