Thank you for the answer! If i understand correctly, given the same image dimension and bit depth, the only thing that matters, is number of channels? So 1024x1024 8 bit texture will take 1 MB RAM if it's greyscale, 3 times as much if it's RGB and 4 times as much if it's RGBA?
Yes, that's correct.
Also, what is the better option - to have 3 single channel textures, or 1 RGB texture, in terms of RAM consumption, scene parsing time?
Good question. I never tried to measure it, but as long as we're talking about 3 files vs 1 file, there should not be any noticeable difference in memory consumption or parsing time. When we get to 3000 vs 1000, the difference might be a bit more noticeable in terms of parsing time as there is some small overhead with opening each file, etc.
The overhead is much higher when the texture files are stored in a network location, as there are higher latencies involved in opening the individual files, etc.
So, I would definitely not worry about this unless you have problems with the parsing times and have a reason to suspect that the texture loading might be the cause of those problems.
One of the key points of Corona philosophy has always been that users should not worry about technical details. So if you ever get to the point where 3 files vs 1 makes any noticeable difference, I would prefer to solve this by optimizing the texture loading code rather than forcing the users to store their assets in a certain way.