Based on the colors & the shape of the flowers, I was thinking they might be late 1960's/early 70's. If there is one you are willing to part with, I'd do a burn test to make sure they are 100% cotton. Poly & poly-cotton blends were all the rage back then & speaking from experience, it was a nightmare trying to harvest the fabric & turn it into baby quilts. Definitely need to know if you should be ironing it on a lower setting so as not to damage the fabric if it's not cotton.
Normally, I'd recommend pairing it with an orange, but I tried that & it was not enough contrast with the yellow HST's. What about just going with a solid dark brown?