i would say so too. Second best answer is...
Size is yet another aspect after color, too. It is not important that it is a monster size dildo - might even scare her off. But you should make sure it`s at least somewhat bigger than you(rs). My answer is:
1. black/dark
2. realistic look and feel
3. bigger than yours, especially concerning girth
4. preferrably rideable (= with suction cap)
5. optionally with a harness girdle, so you can ride her doggy-style with it while she is bent over forewards and watching an ir-porn-clip of a black guy and a woman that reassembles some of her visual traits doing doggy.
Don`t be reluctant to buying a realistic looking black toy - it is just a toy after all!
She won`t be upset about it provided she wouldn`t, if it was any other sex toy. But maybe she will be curious about your choice - a good opportunity for bringing up the topic. Anyway, rather not do it bluntly right from the start.
Some possible initial conversations:
She: Oh my... I think I don`t want to use this!
you: You don`t have to, but now that you have it... let`s see, if the both of us will enjoy it. If not then at least we`ve tried. We won`t know, if we don`t try, right? But i do well imagine that we both will enjoy it and like to use it on you in our sexual play, sometimes.
She: Why do you give me a sex toy? (Isn`t our sex good enough for you the way it is now?)
you: Our sex life is plain great as you are the most beautiful/erotic/sexy woman i know. That`s why i will always give my best to sexually entertain you and give you pleasure - because i love you and you deserve it! By the way, i will love to see you get off on it. Seeing you get off makes me always hot as hell, maybe even more than you. Plus, i am satisfied when you are satisfied. So i am pretty sure we both will like it!
She: Thank you, but I had preferred a cute discreet looking pink model and not an ugly ungainly dark thing.
you: i wanted to buy you a smaller pink vibrating toy first, but then i heard that many women suffer from decreasing pleasure from natural vaginal sex once they are using vibrators and get used to cumming from vibration, and i don`t want this to happen to you! So i thought, in order to not disaccustom you from the pleasures of having natural sex, a dildo with the most realistic look and feel will be the best choice.
She: Why such a big one? I don`t think it will feel comfortable to use it.
you: It is not that big at all, just slightly bigger than m(in)e. That`s why i am pretty sure you will be able to take and enjoy it. After all, it wouldn`t be an advantage, if it was same size or even smaller than m(in)e - that`s what you can have from me anytime anyway. ImO a bigger size provides more pleasure, don`t you think? And i get sooo excited and aroused when i see you well-pleasured. That adds to my own pleasure too. So, i am pretty sure we both will enjoy very much to use it on you!
She: I don`t think I will like to use this. It is like a real dick and I don`t want a differnt dick - I want yours only!
you: That`s funny! i mean, come on, it`s but a toy - nothing more, nothing less.
(giggles) Let`s just try it first and decide afterwards if we like to go on using it or not, okay? Anyway, you don`t have to look at it when i use it on you.
She: Why a black one?
you, lil liar: i really didn`t think much about color. By the way, it was the only color they had in stock.
you: Here`s a little intimate present for you. From me.
She, after opening the package: Wow! Gimme that big black dick! That`s exactly what i`ve always wanted. Only... the version with a man attached is better.
(giggles)
But seriously...
Make sure not to be too obvious right from the start. Use "harmless" expressions, like "the toy", first and don`t say things like "big black cock" right away and go more graphic only gradually (e.g. from "the toy" to "the pleasuremaker" to "your pleasuremaker" to "the (other) dick" to "your other dick" to "your dick" to "the/your big dick" to "the black dick" to "your black dick" to "the big black dick" and finally "your big black dick"). Always observe your woman`s reactions and don`t push it too much/far.
And again:
Don`t be reluctant to buying a realistic looking black toy!!!
Good luck, make a good choice and have alot of fun with your woman!
Kind regards.