The question of tipping has kind is really several questions.
Firstly 'was my lesson so good I would like to give additional reward in the form of money'. I don't think this is an area that demands a lot of discussion on its own. Do what you feel.
One is whether it's an ethical issue 'I should tip my ski instructor so they can make a better living'. This is complicated. I don't think you should ever feel obligated to tip for a service which was objectively speaking poorly performed. Most, but not all, ski instructors are poorly compensated - some make a living wage without gratuities (e.g. higher level pros at Yellowstone club, Aspen; high level European ski instructors). Then again, the cost of living in and around ski areas is absurdly high, and your tourism/vacation home directly contributes to that phenomenon even while it pays their bills.
There's also the question of what you can afford - I don't think a lavish tip should be expected from people who have saved up for a one-off experience. If you're the CEO of a fortune 500 company, you should probably pay a decent size gratuity if your service was good. Some very wealthy people still operate in their lives as if they live in total scarcity - they don't tend to be great clients or customers in any hospitality business.
Another question is 'how high maintenance of a guest are you?' The truth is, not everyone works their ski instructor the same amount, and some guests like to demand their ski instructors perform services that are well outside the job description and sometimes taking up time outside of their typical working hours. If that's what you want to do, I feel not tipping is extremely rude.
The other is 'what kind of relationship do you want with your ski instructor'. Every big ski school has guests who have bounced between instructors for private lessons every year without having a regular pro. Sometimes they're unlucky. Sometimes they ski with people who don't know how to cultivate long term relationships. But sometimes they tip poorly, and may also be very high maintenance. That's fine. But consider that the instructors themselves have some discretion about whether they ski with you - so if you want a very good person to come back and teach you year after year, some aspect of the experience has to be good for the instructor too.
It's very hard for a guest to understand the effect some of their choices have on instructors. Consider, in the Colorado example: if you book a half-day afternoon private product it is objectively difficult to consistently staff that lesson with a top-tier instructor, if that's what you want. Why? Because they're desireable enough to clients to sell their services to them for full days, consistently. They may even have to forego 3-4 hours of work they otherwise could have got to be able to make themselves available to teach that product. You should probably tip if you're going to do this.