GT I think your issue could be because you're only expressing once a day? Logically it feels that the longer you leave it the more milk you'll have but I think the opposite is true. It's only by stimulation that you'll get any milk. The turn from yellow to white sounds like you've gone from producing colostrum to milk so you're on the right track. When J was born even though he was too wee to feed the MWs had him on my breast for virtually all day! One of my MWs was really inspiring as her firstborn had strep so was in the SCBU for 20 days and she wasn't able to start BFing until day 21 but managed to keep up her supply by expressing. She was the one that got me to preservere.
Even if baby won't feed on you it might be worth offering him the breast or just lying him on your chest for skin to skin? - it's only by stimulating the breast that you'll get milk. The only day I've had problems with my supply (and it was terrifying - you have my total sympathy) was when we tried to do too much (register him, visit both of our offices and show him off, and go shopping) and I left it 5 hours between BF or expressing and without the stimulation my milk supply had really started to disappear - I normally get 100-150ml per express and struggled to get 20ml - and this was just from one day's cock up. MW told me the best way to fix it was to express or have J on the boob every two hours for half a day - and et voila it was back.
You're doing amazingly, your milk is there. But it might be worth upping the frequency? I find mid morning is when I get the most out by expressing.
As for us we went to the docs - the green poos seem to be indicating that his bowel is still immature and is struggling to digest the lactose in my milk. Will have to keep an eye out for lactose issues. But the boy seems happy as a sand boy other than having scary looking poos so am trying not to worry. And am NOT going to be asking Dr Google anything until we get the stool sample results back as I don't need to stress myself out.
Walking back from the bus stop from the docs was like wading through an ice storm / gale - god am looking forward to moving south!!!! The forecast looks shite for the foreseeable - still - we have a full fridge, tinternet, good books and Greys Anatomy on the TV so I have no intention of leaving the house for the rest of the week.