Christmas fabrics would probably look good with a solid red or green sashing, without the black. I don't think black looks very Christmassy.

I agree Quilting Cat, the only reason I thought of going w/black (and keeping it narrow) is because I'm afraid a green or red would clash w/the green or red in the blocks...there are many different fabrics and therefore shades of those colors, and even one block that is made in blues. So, I thought black would be the one color that would not clash...if that makes sense. These blocks are from a swap I did many, many years ago (like 9 or 10 yrs ago), so it's a sampler type quilt.

Why not just use the black for your sashing?

When I made a quilt of sampler blocks, I framed each block with a color to match the block. Then I sashed mine in white.

It is sooo cute. My granddaughter named it "Quilt Show".

If you have a design wall, put the black fabric on the wall and then pin the blocks in the order that suits you to see how you like it.

I like using a dark sashing. I like the way it showcases the blocks. But I often use a very dark color, such as a navy, a deep burgundy or brown or even a very dark green. I find that the very, very dark color gives it a bit more warmth but being very dark it doesn't actually show as color. But, as with so many things, lay your blocks on it and leave the room. Each time you enter, think about what you see. It is just ok or do you really like what you see.

that will work

I think the narrow black would give a stained glass effect and it would 'settle/calm down' all the prints in the blocks.

Another option would be to put a flange around the blocks instead of a border. That has the advantage of allowing you to go really skinny and avoid adding extra width, if you don't need it.

Could you audition a charcoal? Might be a softer look than black.