I’m not sure if there’s ever a standardized name for colour palettes like there is for specific colours (IK Blue for example). This poster uses complementary colours (purple and yellow being on opposite ends of a colour wheel). Most of the posters I’m seeing on the Behance project are monochromatic with a grey background. You’ll find more of the same style by looking for “acidgraphix”, which is the current hip design aesthetic on social media.