What you want to do is to make 4 QST's (Quarter Square Triangle blocks). That's what those 4 multi-colored blocks are called.
There are many ways to make these, but the one I prefer the method explained here (see below for measurements):
http://sewhappy10000.blogspot.com/20...orial-tri.html
And ignore the annoying music. ;-)
For future reference, here's the exact calculations:
You want to first cut the squares for these blocks 1.25" larger than the finished size you want (which in this case is 6"), so you would cut them 7.25" and then use the method in the above link.
Now, I ALWAYS make them larger and then cut them down to the exact unfinished size.
So I would cut the squares 7.5" or larger, use the same method in the link, and then trim down to 6.5", which is the unfinished size needed for YOUR Ohio Star block.
Since you mentioned that your QST's are only made of 2 colors, then you would need to start with 2 squares of each color to make the 4 QST's for the block.
The obvious benefit is you never have to deal with triangles or bias edges.