For example, if an iPhone user messages a non-iPhone user in Apple Messages -- the default messaging app on an iPhone -- then the text appears to the iPhone user as a green bubble and incorporates limited functionality: the conversation is not encrypted, videos are pixelated and grainy, and users cannot edit messages or see typing indicators.
Not everyone has an unlimited messaging bundle, especially when it comes to MMS, so showing things in different colours dependent on whether it's using the data plan, or not is a useful feature.
I guess if you've got an iPhone you shouldn't be worried about that though, and instead be considerate of the feelings of people that can only scrape together enough beans to get an old Android Phone.
Or maybe, just maybe, you could both use a cross platform messaging solution that uses the data allowance. Something that you might not know was necessary if there wasn't the distinction between iMessage and SMS/MMS in the Apple Messaging app.
This really does seem to be scraping the barrel.