There are variations out there on mitred squares (on old technique): this is how i like to do them, and two successful colour combinations.

This pattern includes two sizes:
the baby blanket uses three different colours (7 balls in all: 2 balls of each plus an extra for the main border colour).
the throw uses twelve different colours (25 balls in all: 2 balls of each, plus an extra one in the border colour).

Once you understand the construction, it is easy to make changes to suit yourself, like adding more squares, using more or less colours, or making the squares bigger or smaller. Of course, this will change the yarn requirements.

As the squares are knitted from stitches picked up from previously knitted squares, there are no seams (but lots of ends to thread in).