Technically, all so called true colour images are 8 bit. It depends on whether you're counting the total bits or bits per colour channel.
A true colour jpeg, for example, is commonly called a 24 bit image, because it has 8 bits of colour information each for the red, green and blue channels. So, 8 bits per channel times 3 channels equals 24 bits. It can be confusing unless everyone in the conversation is using the same assumptions about what bits they're actually counting.
Let's call the true colour images you would normally want to use for textures 24 bit images. Image formats that fall into this category would be tif, bmp, tga, jpeg, png and quite a few others, but those are the most common ones. Note that the tif format (amongst others) supports alpha channels, which then takes it up to 32 bits, as the alpha channel occupies 8 bits.
And yes, if the image is 24 bit (what you're calling 8 bit), when you load it into memory, it will still be a 24 bit image.