It is not normal for you to have the slight yellowing part in the eye. It is a sign of eye disease. You may have the problem at the liver. You should go to the hospital to let the doctor have a check on your eyes. It is very necessary. If there is any problem at your eyes, you need to treat it as soon as possible.
I have to aware you that your symptom may indicate there' s problem in your liver, which can be diagnosed as jaundice. As I can't get your details, you may do test in hospital.
Jaundice can induce the yellow stained of your skin, sclera and other tissues. When it gets worse, your urine, phlegm, tear and sweat can also appear yellowing. When the erythrocyte died, the heme in hemoglobin will be accumulated in Kupffer cells of liver and translated to bilirubinIt and will be expeled finally. The disease forms when your liver can't deal with the appearance of erythrocyte or it can not expel the erythrocyte.Thus, it may not be an eye disease but a kind of liver problem.
For my advice,you'd better go to do some test to so that you can deal with the problem early.
Well, for your situation, I have to say that you may get yellow eyes in some degree. First you should know that if your eyes take on a yellow tinge, the reason may be jaundice. For the causes, smoking, iron deficiency, coffee can just lead to yellow eyes. So you can just need to be careful about it. And in common, you can mix tomato juice with salt and black pepper. And drink it on an empty stomach and typically in the morning. Also, just take more foods which are rich with iron.