My son is now 2yrs old and he has S26 from birth. So far he doesn't have 痰 (unless sick) but his 'ng ng' is quite hard sometimes. We once wanted to change milk but it seems not very serious. Besides, my son doesn't drink much water so we're not sure if it's the reason of hard 'ng ng'.
After 6mths old, we let him drink more juice+water, soup, vegetable and fruit, his 'ng ng' is better and so far there's no problem.
It's true that not all BB can drink S26. I know two friends' BB are ok with this - no 痰 and 'ng ng' are soft. Some said S26 BB are very fat but my son and one of these two friends' BB is just average size. You know each BB's 體質 is different so you should see your own case only.
My son's 'ng ng' is also 綠綠黑黑咁既色, 仲好難聞(酸酸臭臭咁). The nurse said 綠綠黑黑咁既色 is ok when they're young. It'll change to brown when they're older.
Firstly, you have to make sure your BB drinks enough water. However, if you find your BB