Swish curtain hooks are available in three colours:
By far the most popular Swish curtain hook is the white version and as of 2012 the other two colours were discontinued, although I still have some stock left. The only curtain hook which Swish manufacture are for curtains which have heading tape. Generally I find these curtain hooks to be reasonably robust and suitable for most domestic curtain weights.
I would think that the brown version of these Swish curtain hooks would have been used in conjunction with the brown version of the Swish Furniglide curtain track which was often used on railway carriages, and would have matched the old wooden decor.
NOTE sold in quantities of 1, photo for illustration.