Seamless join

I have searched online and couldn’t find it, but how do you join two blocks seamlessly? What color would you use? Is there a video somewhere? I am sure this is an easy answer, but as I learned to knit online…I don’t know much yet…Thank you so much!!!

If you do them as separate blocks that you want to join, you’d use something like mattress stitch (amy has vids of it [B][COLOR=purple]here[/COLOR][/B] just scroll down to the finishing section), but that will leave a ridge on the back side of your work, just bear that in mind.

Thank you…I didn’t realize it was called that…that helps!!!