Yes, it needs to be HTML because this field gets uploaded to our website.

Thanks Andrew, it looks weird, but it works!

This was my final result:

Code:
IF({quantity} >= 1,
CONCATENATE("<font size=",CHAR(34),"4",CHAR(34),"color=",CHAR(34),"green",CHAR(34),">In Stock</font>"),
CONCATENATE("<font size=",CHAR(34),"4",CHAR(34),"color=",CHAR(34),"orange",CHAR(34),">ETA 2-5 Days</font>")
)
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Lance Tennier
TDL Canada