I'm in the cutting stage for a very scrappy flying geese (columns with sashing between) and can't decide on the "sky" fabric (all the same, and maybe the sashing will be the same too.) I'm thinking of the undyed muslin but wonder if the quality is good enough. And will it be too plain? Is there a difference in muslin quality from Joann's vs. an online store? Beige tone on tones are hard to find, especially online where you can't really tell. Please advise.

I would go to Joann's or any other store that sells it and feel it for yourself. There are many grades of it.
I wouldn't order online unless someone else here may know of a good experience.
I love using muslin! Especially when hand quilting- it makes my stitches beautiful~
I also use it for backings, and a lot of block pieces.

The muslin would be great. You must use a good quality though. I like Kona the high end stuff. The Egyptian cotton is the best thread count there is. Can't wait to see the finished product.

I buy mine at Joann's by the bolt.

I like muslin, there are different qualities. Marshall's Dry Goods has a tea-dyed muslin that I use a lot for a more natural/vintage look.

muslin comes in many many different (grades) qualities, weights, thread counts; if it is a good quality, nice feeling muslin use it...always pre-wash muslins; they are a lesser thread count and will shrink a little more than normal quilting cottons at times. muslin is very nice to work with and gets softer and softer with each laundering

I avoid muslin at any cost unless I am looking for an antiqued look.

I absolutely "love" muslin! I use it for most of my quilt backs and am currently using it in 2 different quilt tops. Love it, Love it, love it!!!

I use muslin a lot, but be sure it's a good grade and prewash it if you are using it as part of your quilt. I use a lesser grade for projects where you won't see it. I'm making turtle pillows for a community service project and will use a less expensive muslin for the bottom of the turtle. That way I'm not wasting expensive fabric on an area that will not be seen.

I think it will look great with your geese!

With prices rising, I've decided to start using more muslin in my quilts. I love the quilt shop quality fabrics, and this will help me stretch my stash out longer. I love the Kaufman Premium Muslin and the Southern Belle Muslin - both are 200 thread count. I've gotten them for very good prices. Higher than the Roclon muslin at Joann's, but much less than adding more of the prints to the quilt.

just use good quality I used it in my log cabin