Mineral deficiency perhaps. It could also be uptake which means the soil is too basic aka high PH.
Since the fertilizer you are using should have these minerals then I would guess its an uptake problem like PH or much too water. Over watering can lead to nutrient uptake problems.

Pale leaves means something wrong with chlorophyll and several minerals are involved in its production.

http://edis.ifas.ufl.edu/EP325

Searching google images my help you as well.

its coulb be Beet leafhoppers

Here is a link that might be useful: Tomato-growing-problems

My indoor plants had pale/light green leaves so i decided to feed them miracle grow. Since then they have become a dark rich green, shot up, flowered and are now producing fruit. All this in the space of 2 weeks. I did not change the soil, just fed them fertiliser. After 2 days i noticed that the top leaves were far greener than the pale leaves below. Soon after, the whole plant looked healthier.

Also, i did a little experiment where I grew some tomatoes in an acidic soil that i collected from beneath my pine tree. These plants are very bright green and rather small and I dont think they will do well, but it was just a test.

One good organic way on tomatoes is wood ash if you can verify the soil is enough on the acid side. I add wood ash to the compost pile that also has pine needles and coffee grounds which should balance out a bit. One cannot go wild with it because wood ash and rain water is a recipe for potassium hydroxide aka lye and will raise PH in large quantities. Wood ash that has not been rained on is best since it has all the soluble minerals otherwise, the rain washes it away. I just add a few spoon fulls to a gallon of water.

I get similar symptoms because I'm growing on an extremely alkaline, clay soil. In addition to adding LOTS of organic matter, I also amend the soil with elemental sulfer once per year to help acidify it. Even with all that, the pH never drops below 7.2 or so. Sometimes during the growing season, usually the at the start, plants will get bogged down and chlorotic, despite having plenty of fertilizer. A litte iron sulfate greens them right up and gets them growing, not so much because they lacked iron, but because the sulfate helps acidify the soil. I buy a generic brand, but a more common brand of iron sulfate is Ironite. If you Google "Ironite" you'll find it's pretty controversial, but I still use it judiciously since I've yet to find any alternatives.

dirt_poet,
In the Chicago area we have such a thing called Lilation Park.It will knock you out in spring. That is the flag ship of high PH loving plants. We don't need much lime here.
Compost also helps with acidifying. If you can make your soil biologically active they will produce CO2 which will become carbonic acid in the soil. Its the same reason why coke is cloying when it is flat without the carbonic acid bite.
I did read where someone in California dumped so many coffee grounds on their soil that they altered their entire flora with earth worms and all , not to mention PH.

I had the same problem earlier during a fast growth period. I know that potted plants which do not need repotting sometimes show pale or yellow growth when they need magnesium. Plants will also show leggy and pale growth when they are iron deficient. I agree with the ironite suggestion, if you think iron is the culprit. I was able to fix my problem with a dose of epsom salts, which contain magnesium. I used the drugstore kind, but I think Espoma makes an organic salt that may contain more trace nutrients that the pure salts wouldn't have.