I don't know that it's as cut and dried as matching a child directly within faith/heritage etc, only that it is preferable given options.
We adopted our DS, who came to live with us at 4 months old, with the guidance from SS that we raise him with knowledge of catholicism, as this was requested by birth mother. We know nothing of catholicism and made it patently clear that this was the case, but that we would respect birth mother's wishes by encouraging DS within his education, and advising him that his birth mother wanted him to know about it.
It's more about respecting the fact that this child, as much as he is ours, is the product of two different families, and we need to integrate the wishes of his birth family where practicable, possible and appropriate to our family.
In terms of matching and hair colour etc, it is definitely something that is taken into account. My SW explained this to me when, the month before we were matched with DS, we were told that we had an unsuccessful link with a little girl.
She was 5 months old, white, with no known health issues (ie - a very sought-after group) and we were one of 9 couples linked with her. All 9 couples were deemed to be "suitable", so it came down to various factors. she was, apparently, very dark haired, and as DH and I are both quite fair, this was one of the reasons that we were not prioritised. She was placed with a family who "matched" her more appropriately, visually.
Equally, we were one of 8 couples who were linked with our DS, and looks were a part of what was considered. adopted children need to "fit in" and sharing ethnicity and looking like your adoptive family can certainly help with that. whilst it is not the most important factor by any stretch of the imagination, sometimes SWs and family finders have to look for tenuous reasons to filter out the many prospective adopters who are put forward for each child.