is it a blend or a perfume?
A botanical perfume is a combination of science and intuition. Differing from an 'oil blend', care is given to balance the fragrant story and get the volatile plant essences to affix to the skin. Commercial perfumery uses synthesized ingredients to 'fix' the scent to the skin, they use very little actual scented material and a lot of filler, and often have hormone manipulators.
Colognes and Perfumes are related, but perfumes have a higher concentration of 'base' accords, while colognes are more fleeting because they have more 'top' notes.
In perfumery the base is what fixes the fragrance to the body, and the essences tend to be 'heavier'. For example, vetiver and patchouli are base notes that give a fragrance longevity on the skin... while citrus notes like bergamot are top notes: ephemeral.
Just combining vetiver and bergamot don't make a perfume -- it makes a lovely oil blend, but it will lack depth, fullness. Expert care can transform accords like Fougeres and Chypres (which often contain vetiver and bergamot) into a proper perfume (or cologne).