Thank you for reaching out to us.
There is no obligation to sleep on white sheets for first relations, and it is also not obligatory to seek out dam betulim. Sometimes, it can be important not to look for it, as when the couple did not complete relations on the first try.
Note that the sheets supplied by hotels are generally white. Therefore, a couple staying in a hotel may wish to bring colored sheets to avoid questions of stains.
Please let us know if we can be of further assistance.