black will recede it. pick a nice zinc color or try Kendall Charcoal. that goldenrod planter in first pic is a beautiful choice w/your colors. I would two of those next to the door, in the shape of those black ones.

try some coleus plants and impatiens, since they like shade. some ferns might do well also.

this color coleus w/the yellow or the black planter

these ferns would also work. and even this blue door would work w/your color palette

Yes, black will look too dark. I actually really like the cream.

I agree that black would do nothing for the space. Presumably there is some light in it at night (no fixtures are shown on the photos). If not, you might consider adding some, perhaps wall sconces. The white door color may be the best choice, if there is not another light color that can be picked up from the stone colors.

What is a bit odd in the photos is the reflectivity of the glass in the door and the sidelights. It almost seems like a privacy coating intended to give a mirror-like effect. Is it clear glass?