Looked up the number in my list and found it. A sort of teal/sea blue grey. Oddly, it is the colour I just used for some curtains. I had a similar problem with matching and had to hand hem because of the show through on a machine hem.
There are lots of those sorts of colours in fabrics, but that seems to be a standalone in the threads.
The one next to it, 553, is darker and greener.
The next in greyness is 788, but that is definitely grey and lacks the blue.
224 is the same depth of colour but in a greyish green.
Nothing else comes close. Don't forget darks go in lighter and lights go in darker. How does it look in the fabric?