These are around $125, which is less than half of what O'Connell's charges for theirs; given that, but also given that these would see only light wear (perhaps 6 times a year), would these be acceptable in light grey for pairing with a navy blazer? Thanks in advance.
First, kindly add a link to the shop's website where these trousers might be shown, so that we can see what you are considering.
Second, if you are unsure about this company, ask them to send you a swatch of the material they use in their grey flannels. This will give you an idea of how heavy or light the flannel is, how mottled it looks, etc. You could also ask them if the fabric is 100% wool, a blend of wool and cashmere, or a blend of wool and polyester. Personally, I also like to find out where the clothes I purchase are made, since the country of manufacture often makes a difference in terms of quality.
Third, you can search this website to see if there are any postings regarding Peter Christian flannel trousers. I should also add that looking for a pair of grey flannels at a thrift shop can be very rewarding. I have found wonderful, and often brand new, grey flannels from reputable makers like Brooks Brothers for a few dollars at local Goodwill shops.
O'Connell's is known to many of us on this site, and they do make very fine trousers and other items as well. I understand that the price is significant, but a pair of flannels from O'Connell's will last for a long time, especially with the light use that you contemplate.
Almost any grey from a light silver grey to a medium Oxford grey would be quite acceptable to be paired with a navy blazer. Beyond that, as one drifts toward the darker greys like charcoal, there is less of a contrast with the dark blue of the jacket, and so, to me at least, the combination would be less appealing.
I literally have at least fifteen pairs of grey flannels (it's a minor obsession with me) in fifteen shades of grey, LOL, and for me, the perfect match with a dark blue blazer is a pair of Oxford grey flannels. Add a crisp white OCBD, a regimental tie and a pair of burgundy shell cordovan loafers, and one can face the world!