When a recipe such as https://www.jamieoliver.com/recipes/vegetable-recipes/easy-tomato-chutney/ refers to "mixed-colour tomatoes", does it mean that it's OK to collect not-quite-ripe ones from the greenhouse or that one is expected to buy some orange etc. tomatoes to go with the red ones?
Oliver appears to be referring to ripe tomatoes of mixed colors, mainly for appearance. He has a separate green tomato chutney recipe for underripe tomatoes.
The mixed colors are somewhat pointless in this recipe, as everything is cooked for 40 minutes with red onions, so any variation in tomato color would be completely lost.
The recipe as written would work with just red tomatoes, and it would work with a mix of red and underripe green tomatoes as well. If you are including unripe green tomatoes, you might need to add more sugar. You would need to make it and taste it.