I am not going to spend the next three hours explaining how Obama and that goat fucking weasel Joe Biden as his vice president made some shady deals with the party in power of my country to start a very devious and corrupt drug war. And I am not going to tell you that I was working as a field teacher at the time of that drug war, That shit got so dangerous I had to quit my job. That said drug war fixed nothing, it only kicked the hornets nest , killed a lot of people, it painted the streets red. It moved money towards a new breed of more violent drug traffickers and blocked legislations that would make drug regulation possible. and that it wasn't just in my country; Obama was a useless hypocrite neoliberal puppet, pure scum. He had the power to make a lot of positive changes and just followed the lead of the people that were really in power in America: The corporations. I am not even very versed in American policy. I'm sure There are American people out there that paid attention at the time might have an idea of how The Obama years paved the way for the trump Era.
Americans live their lives ruled by people who would rather put their balls in a vice and set that vice on fire than to pass regulations on Corporations. Meanwhile those corporations concentrate more international power and either impose or export their corruption to the rest of the world. Your politicians are bought and paid by these conglomerates, they are your government. Your democracy is a farce, your politicians spent decades dictating to the rest of the world what civility, democracy and free market should be. And the moment those concepts are an obstacle to the concentration of power of American corporations all those wishy washy ideals go out the window. America imposed neoliberalism in Latin America. killed thousands in Chile, in El Salvador, in Brazil for their little project and now they have to gall to say the rest of the world owes them everything. What a joke all this is.
I'm sick of it. I'm sick of having dumbass American politics exported to my country. I'm sick of American culture, I'm sick of being worried of who is going to be the new dumbass on power there and who is going to be demonized by their foreign policy. I'm sick that it's a black hole that wants to privatize everything. I'm sick of Sam Altman , Elon musk, Jeff Bezos and Hillary Clinton. I'm sick of the money that flows to the media on other countries outside of America to Manufacture consent and i am sick that you can't even say "FUCK AMERICA" in social media, because you fuckers are so thin skinned you can point guns to the rest of the world and can't even take an insult!
To avoid panting with black is a common truism for traditional painters that will save your saturation in the lower values of your painting. When painting a naturalistic scene in a traditional medium, you are in a loosing war against the cost of saturation. (saturated pigments tend to be more expensive.) Ivory black and lamp black are very cheap pigments, hence the mixture of black paints tends to have more pigment vs medium. Also, Pigments lose saturation over time. so vibrant paintings you made 10 years ago can start to become grey.
The area of your painting where the saturation loss will become more daunting is the shadows. They tend to be a cool temperature and have a lower value and saturation. This is one of the reasons why it's dangerous , especially for a student to use black; And this is the reason why a lot of traditional painters plot their shadows with washes of earth pigments: Burnt sienna, burn umber etc.
The other reason is convenience: Leaving you some space at the bottom and top of the value structure for final touches. Once you reach the floor value of pure black it's hard to go back up, especially if the rest of the values are down with that black. Same for white. If the key of your painting is too high, it's hard to add any detail without just burning the rest of your picture. So keeping some floor and headspace for the final details can save you a lot of headaches! And this is especially true for black paints since they tend to have so much pigment in their mixtures
In digital media it can also be beneficial to avoid blacks, or at least clip-mask them into a black with a little temperature in them at a early stage of coloring. I can't really explain the reason for this exactly, but neutrals and especially black and white have a lot of visual pull in a monitor that displays thousands or millions of colors. Just adding a hint of temperature to your blacks and whites can make them gentler on the eye and keep the colors from becoming muddy*.
(*Muddy colors are a result from disorganized value and temperature structure between your lights and shadows.)
So your teacher was right, he was just either too lazy of busy to explain all that shit!
Edit: I remember my very cruel first semester painting teacher gave us an assignment of making value swatches for 15 hue-degrees of the color wheel. We had to make 10 swatches of low saturation greys (grey mixed with a hint of color pigment) From the lightest we could manage to the blackest. He would make us repeat the whole set if one swatch was "too saturated" or if a value scale was off. IT WAS HELL. I am not sure if that exercise was intended to make us despise black and white tubes or give us an idea of how different the proportion of pigment and value is between painting tubes. I developed an irrational fear of adding black to lower values.