Oh- you sound like me! I laughed when you said you wanted it to look like the ones your grandmother made- how much experience did she have when she made them? Give her some credit for having learned something through her life, so therefore you have to be starting in a different place!
And the place you are starting is a good place. I have to say, when I read your title I thought I was going to be looking at something far far far FAR more of a challenge than this! I love blue and yellow and I think you have done well - try out those darks you mentioned and see how it looks- playing with it is part of the process.
And, of course, don't forget to show it to us when it is done.....
And tell your husband hi from my husband- the brotherhood of quilting widowers........