Below are a couple of good sites to visual signs of nutrient and other ailments of tomatoes. Your leaves are more reddish purple than yellow. I will get the purplish color especially when seedlings have been in the pot too long and they lack phosphorus. The purple will be more pronounced on the stem an underside of the leaves, but the reddish color to the leaves I get that more in summer when it is actually getting warmer. Sometimes it is from mites but it usually is on the underside of the leaves not the whole leaf unless it is severely infected. I have had some of the red colored leaves from temperature changes usually when it is either too hot or too cold. Temps less than 50 degrees F or less than 10 C or over 90 F or 29.5C. It seems to be a physiological reaction to stress. If the tomato is not wilting at midday, it probably is getting enough water.
https://www.missouribotanicalgarden.org/ ... oblems.pdf
https://www.haifa-group.com/knowledge_ce ... _symptoms/
I would look for pests under the leaves
If temperature has been hot, try shading and mulching as well as midday watering to help cool things off
Tomatoes are heavy feeders and should have a starter fertilizer and supplements every month. If you are using organic you may have to go every week. If you used a lot of compost, the pH may be a little high so go with an acidic fertilyzer.
Since you are in the southern hemisphere your seasons are probably opposite of ours. It would help to know what your average daily temps are as well as the kind of soil you have.
Happy gardening in Hawaii. Gardens are where people grow.