Lover of the Night (Guns & Red Roses 2) is by JoLynn Horvath, who thinks that Klaus's eyes are gray.
Dorian has a little fling with an ancestor of Klaus's, who just happens to be a vampire. Before Dorian and the vampire repair to a quiet spot, they have a nice enlightened conversation about how the sex of one's bed partners is insignificant.
A little later, Klaus and his intrepid alphabets burst into Dorian's boudoir to interrupt his canoodling with the vampire, armed with crosses, holy water, Stars of David (this is a PC vampire who is repelled equally by the symbols of all major faiths), and garlic. I really want to know how the Major explained this mission to them. "Your mission is to stop Eroica from getting laid! Here are your weapons - religious symbols and pungent spices!" Klaus himself seems completely unfazed by the fact that his opponent is a vampire.
This gives our vampire friend a chance to say, "Poor mortal fool! Do you think to stand against me? I am the power of the night, eternal and unstoppable. Leave now, while you still can!" Really.
Well, they chase him out with holy water, and a couple days later Klaus proves to Dorian that his new boyfriend is a vampire and Dorian has to choose whether he'll take the vampire who wants him or the mortal who's still pretending he doesn't. Klaus doesn't seem concerned by the fact that this vampire has been going around exsanguinating people and will doubtless continue to do so, he just wants Dorian to make an informed decision before joining the ranks of the Undead.
Dorian thoughtfully explains to the vampire that it's Klaus he really loves, and also the vampire needs to get over his vampiress girlfriend who just died before getting a new sweetie. The vampire is very understanding and sensitive about it and goes away and stops bothering them. Klaus doesn't cave. The End.