The answer is technically, yes.
BUT, as plain tiles have to go through the same processes as the patterned ones, they work out pretty much the same price as the patterned ones. In most cases, you'll be able to find perfectly acceptable plain tiles much cheaper elsewhere.
If you're thinking of using pattern tiles as a border or panel and surrounding them with plain tiles, one option is to use a 'framing' technique such as a border tile to create a visual barrier to separate the two types.
There's more information on tile borders and tile strip here.
If you want to run two types of tiles together, my normal advice is to buy your pattern tiles (or a sample) first and to take them along to a mass-producer (eg Topps Tiles or Tile Giant in the UK) to find a cheaper plain tile in a coordinating colour.
If you're going to do this, bear in mind that sizes vary hugely between different manufacturer. I would caution against buying lots of plain tiles without getting at one with a tape measure first.
This is because one maker's "6 inch / 15cm" tile may actually turn out to be 14.85cm, 15cm, or 15.2cm. This means your tiles won't line up properly.
Tile depths also vary widely - a tiny difference between the thickness or your plain and patterned tiles won't matter. But if your plain tiles are several mm thicker than your pattern tiles, your tiler will curse you and you may end up with a bit of a 'step' between one type of tile and the other.
If you need more help with this, please see my free Pattern Tiles ebook or contact me.