Certified GKH Gardening Expert
Leaf yellowing is most often due to over watering. While they like moist soil, it should not be overly wet. Allow the plant to dry out some between waterings. You can mist the plant if desired to help increase humidity.
Syngonium leaves turning yellow can be due to several causes, but, if yellowing is affecting the older leaves, it is most probably underwatering. These plants do best if the soil is allowed to aerate moderately between waterings; use a bamboo kebob skewer to test for moisture, as if you were testing a cake. Stick it all the way to the bottom of the pot. If it's feels dry when you pull it up, and no soil is sticking to it, the soil is too dry; it should have a faint amount of moisture on it and a few crumbs of soil. And I'm sorry to tell you this, but spritzing is useless, unless it makes you feel good. The plant doesn't care. They are very adaptable plants, and will happily adjust to whatever humidity is in your house. Watering by using a spritzer is not going to get enough into your plant - you should water enough that water runs out the drainage holes every time you water, then let the plant dry down to the state described above.