Hi Juliet, thanks for the question.

There are a few things that 

Yellow streaking and speckling on garlic leaves can be caused by several factors. Water issues both over and underwatering can cause streaking.  Good drainage is important. Nutrient deficiencies could also be an issue:  A recent or new soil test (Home | MSU Soil Test) can help sort this out. Nutrient Pests and Diseases: Pests like nematodes, thrips, and aphids, as well as fungal diseases such as white rot and downy mildew, can cause yellowing and other damage to garlic plants1. Other items like poor air circulation and other stress factors may cause some problems.  Pest and diseases can be a part of the puzzle.  The various potyviruses can definitely be a factor and could affect yield.  Crop rotation, cleaning up plant debris, heathy cloves can help prevent further problems.  The gray/white streak could be the allium leaf miner (not sure about that).  Early harvest of these may be warranted.  Dig one up and look for possible insects, in the leaves and bulb.  Let me know it you find something and we can figure out how to prevent further issues. Check out the following links:

Be on the lookout for allium leafminer in your spring onions, garlic, or leeks | Virginia Ag Pest and Crop Advisory (vt.edu)

Garlic - POTY Virus Signs & Symptoms - Cooperative Extension: Insect Pests, Ticks and Plant Diseases - University of Maine Cooperative Extension (umaine.edu)

I hope this is helpful.