That is roughly correct. There is typically a bayer-mask filter on a grayscale sensor, so any given pixel is actually only either blue, red or green, but then

That is roughly correct. There is typically a bayer-mask filter on a grayscale sensor, so any given pixel is actually only either blue, red or green, but then a mixing algorithm is applied and you get the full resolution with the appropriate mixing. Of course, there are a variety of filters and a variety of algorithms, so the exact mix will vary across different technologies, but roughly speaking, yes.