I think I'm going to have to rely on your eyes, because in the photos the cedar colour Barker belts look much lighter and thus closer to my eye (especially the Barker cedar grain belt, is it really that much lighter than the grain or is it just a trick of the light).
So is the John Spencer really a closer match? Because the Dovedales are a light, yellowy tan and the John Spencer belt in the photos seems like a darker, redder brown.
Please forgive my hastily assembled photo. Now that I have looked at the actual boot along with the belts I am inclined to agree that the John Spencer is not the best match. The belt at the top is the Barker conker belt, followed by the Barker Cedar, but the best match would appear to be the British Belt Company Miller in Tan . The grain isn't exactly the same but it is a pretty close match. I don't think it is essential for the colours to be exactly the same. Let me know if I can be of any further assistance!