I don't know why I thought to add some yellow food colouring but I did. It was a rather generous sample so I didn't wanna chuck it, I decided to experiment with it. From my past experimentation I have realised you don't need a lot AT ALL, food colouring is really concentrated so you need a tiny amount to turn something yellow. I added a small drop, stirred then swatched. I repeated this until I thought I got an adequate amount of yellow for my skin without making it too jaundice-y. I think for the amount of foundation I had in the tub I used around 3 small drops. 

I tried it on my skin and was thoroughly impressed! It was perfectly mimicking the undertone of my skin and it wasn't too overly yellow! So I came to a theory as to why it worked so well for me this time. I think it was because the original foundation was a good few shades lighter than my skin tone, usually when I buy a foundation it's close to my skin tone but not yellow enough so when I add food colouring I think there ends up being too much pigment and it becomes too dark or too ruddy or ridiculously stupidly yellow (or it could be the obvious fact that I've used too much food colouring). But (may be) because this foundation was a good few shades lighter than my skin tone I was able to build up the amount and density of colour that I needed. I dunno! I could be way off here, but this sample has worked so well for me, people have complimented plus I've used it all up almost!

Left swatch is with food colouring and right is the original NC25.

I think some South Asian skin tones are really tricky to match foundations to, because our skin has a mix of undertones, we are yellow but not orange. My/our skin also has olive brown tones (think of actual olives and the variety of shades and colours they come in) mixed in with yellow, so orange doesn't look right on it, it's gotta be yellowy. Also noting the discolourations we have as well! There are a particular group of us South Asians who fall under this particular mix of tones who struggle to find matching shades, MAC doesn't really carry a shade for us, there are only a few shades that have this particular mix of tones (like F&B in C3 IMO). Nars Stromboli is also a good example but it isn't golden enough.

My sister happened to have a full bottle of MAC Mineralize NC25 (she also feels it's not yellow enough for her) so I've included it in the pictures and swatches so you can see shade and swatch comparisons of the original NC25 and the "yellowed up" NC25. 

So to summarise my experiment, I added food colouring to a shade that was a few shades lighter than my skin tone where I would normally add it to a shade closer to my skin tone. If you try this tip please let me know how and if it's worked for you. I'm always trying new things and sharing it with people so would love to hear your feedback! Hope this was helpful or at the least interesting!