
Here's a gorgeously simple idea from
Home Handicrafts (Mary Harding, Octopus Books, 1977). It's a rainbow bedspread, knitted in simple garter stitch - "Easy enough to knit without looking - although of course you can knit while watching television! Actually, the more exciting the story is, the faster your needles will click".
The bedspread is worked in strips and then
joined together with a row of crochet. The bedspread in the book is worked in rainbow stripes and then joined with a black crochet border as a contrast. There's also this sophisticated version worked in shades of red:

What a brilliant stash-busting project!
The rainbow bedspread in the book is made of out 22 strips, each 16 stitches wide, and 140 cm long. You can work each strip to the length that you want, but make sure that each strip has the same number of rows, to make it easier to
crochet together row by row.
Once you have worked the required number of strips, and crocheted them all together, work 3 rows of crochet round the edge of the bedspread, working 2 or 3 stitches in each corner stitch so that the corners will lie flat.