Do you want a romance with a humanoid alien?
Why not a human?
Do you like another skin colors? Green?
People love Liara mainly because she looks like a woman with blue skin.
If she was different, will people romance her?
What type of alien do you want?
It's not based on appearance for me: I mean, I can find a design aesthetically interesting but it does not factor into my decisions about who I'll romance as that is dependent upon whether or not I like their characterization. When I'm roleplaying, said characterization also has to fit well with the character whom I'm roleplaying.
As I didn't find Liara interesting enough to romance based on her characterization, it is very unlikely that I'd have been more interested in her if her appearance had been different.
As what type of alien I'd like, I'd like a drell or turian as romance options because I find their cultures fascinating and I see romances as a way of expanding upon it. A way to do this is by exploring the different customs of courtship
Example: In the romance with Garrus Vakarian in ME2, there is a headbump between him and the character before the screen fades to black. There were also bits of information about turians flirting and such. Basically I thought it showed an amount of interesting bits about how a relationship with an alien could be like. I genuinely thought this was intentional and adorable. In ME3, however, this seems to have ebbed out and the interactions basically became human even when logically I do not think they should. That was something I didn't like because I felt it took the alien aspect out of the relationship.
I'm curious towards the new aliens that'll be in the Andromeda.