"They have our dark blue suits."
Translation:De har vores mørkeblå jakkesæt.
We can only actually guess that jakkesæt is plural here - the sentence does allow for a communally owned suit as well. It would only be 'mørkeblåt' in the sentence 'et mørkeblåt jakkesæt'. Or 'vores jakkesæt der er mørkeblåt' (our suit that is dark blue), but that is really clumsy. I've spent ages now trying to find a satisfactory explanation for this as my (theoretical) grammar is QUITE shabby, but I haven't been able to. 'Mit mørkeblå jakkesæt' (my dark blue suit), which as opposed to the above is clearly singular as it employs the singular possessive pronoun 'mit', and not the plural 'mine' also needs 'mørkeblå'. I'm no help, I'm sorry!