Based on the images you've shown, where the main colors are the shades of grey, I'd call it grayscale with a single accent color, in this specific case, the accent color is orange.
You could also call it black and white with a single accent color but that might lead people to believe that only black and white were used rather than shades of gray.
Something similar can be seen in these ceramic items:
If you were talking more about something like this tea kettle:
It would be the opposite - orange with grayscale accents.
If you're using multiple shades of the same orange (same color, different amounts of white/black), it would be "monochromatic", like the image below, which is an underpainting of a finished painting: