Welcome to the Bunnings Workshop community @Allysyn. It's wonderful to have you join us, and many thanks for your question about these Monsteras.
It's potentially just a slight bit of variegation to those leave. We do occasionally get stock with unusual attributes.
Let me mention @Noelle to see if she has some thoughts.
If you are concerned at all, you can return the plant to the store. Alternatively, you can hold on to it as we have a perfect plant promise, which means all our plants are guaranteed for 12 months. If you're not 100% happy, return your plant (with receipt), and we'll refund it.
I think Mitchell's right - it is a natural variegation on the leaves. It certainly doesn't look like disease or anything 'sinister'. Yellowing along the midrib or edges of leaves could be indicative of nutrient deficiency but this plant looks completely normal. Golden variegation is quite attractive.