Not generalising in the least: I'm a man of the people who interacts often with the common man - particularly the rustic and bucolic variety (from the Auvergne in Deepest Darkest France to the dusty hinterland of rural Victora and New South Wales).
Everywhere I've ever lived, I've had conversations about animals (most of which I've initiated, I admit - and most of them before I went veggie), with folks ranging from French eleveurs de boeuf to Melbourne barristers and stock analysts: their lack of awareness of the complexity of animal sense organs (and their ignorance of animal awareness research generally) is astounding.
It may well be that you've never met anybody who thinks that all animals see in monochrome - maybe you're young, maybe you don't get out much, or maybe you don't have discussions about animals much. Fortunately, the 'animals see in black and white' trope is dying (as bad ideas should), but it's not dead.
To give you some context: I'm so old that when I went to school we were not allowed to use calculators (mine was the last generation to use trig tables). If you polled people my age (especially outside metropolitan areas) I reckon you would get >50% of them declaring that animals see in "black and white" - that's certainly my anecdotal experience.
Lastly: what makes you think that dogs see in monochrome? As far as we can tell dogs see the visual spectrum in the same way as a red-green colour-blind human does - they have both rods and cones in their visual apparatus, but with different sensitivities than humans' (same for cats, but carts lack cones that filter for red).
Of course we are only using "We can do this, and we have these cells" methods to make that call: as with some migratory birds that can 'see' magnetic fields, dogs and cats may have senses of which we are not yet aware. Cats certainly act as if they know something we don't.