Way to ignore the actual meanings of 'dull' in order to find the results you wantSeriously? Yes, ND filters decrease the intensity of light hitting your lens. It absolutely does not "dull" the image unless you bought a cheap ass filter. The image is still properly exposed. It just allows you to open up the aperture or lower shutter speed to get the effects you want and still get the exposure right. The important part of a ND filter, it filters the light the same across the entire color spectrum, so there's no color bias added to the image.
You can also get tinted filters, which intensifies certain colors. If that's what you're going for. I don't recall any teal filters, however, but I never had a purpose to look for one. I'm sure they make one. Seems like it would come in handy if you wanted to emphasize turquoise. Or maybe Trump's qualities.
Edit: Not familiar with a filter that would be desired to be teal, but some of the old fluorescent or incandescent light compensation filters might end up being a pastel version of that. The ones I'm most familiar with (FL-D and FL-W) both appear magenta to the eye, but we used some pretty strongly tinted filters for black and white when that was still a thing (yellow and red filters) so there might be a teal filter out there, or maybe a stack of a green and a blue filter. Can't really help you with information useful in your effort to denigrate and belittle my viewpoint, though - not familiar with an actual teal filter