I bought all white linen sheets (found some single sheets real cheep and cut them in half) and blankets(also single bed size cut in half) 13 years ago when I was pregnant with ds. Was planning on waiting till he was born (didn't know gender) before buying a little cot coverlet.
In the end I was given one that was patchwork colours are mint green, baby pink, baby blue, white and lemon.
So all neutral and worked just as well for ds and dd.
I recommend to keep everything as neutral as possable and funk it up with accessories when buby is born. Such as a floor rug in gender specific colour of choise, cushins, wall decorations.....I'd chose something that will work just as well for a toddler.
Really they don't stay babys for long at all and before you know it they are in beds.

I recommend single bed sheets and blankets cut in half. They are a little bit bigger so there is room to tuck baby in nice and tight.