Generally speaking the 'colour' of the machine doesn't dictate QUALITY. No brand is better, I've worked on all 'colours' for the past 3 decades.
This gets down to simple pencil/paper comparisons.
You write down what the green machine cost( include taxes !) and then see what a 2-3 year old one is worth( NOT selling $, true cash deal $$ !). Now write down the true cost of the orange EQUAL machine(same HP, deck, features). See what the difference is.....that's the bottom line.
Say the green cost you 5,000,but now worth 4,500. The orange is 6000 ,'out the door'. 6,000-4500 is 1,500. So IF you sell and buy, it's cost you $750 per year to 'rent' the green machine. OK, don't KNOW the real numbers but you need to do the 'math'.
Don't just say the math in your mind, WRITE IT DOWN ! We can make better choice when we SEE the numbers.
As for WHEN to buy/sell, obviously machine are higher priced in Spring than Fall. So you should buy in Fall, sell in Spring