The desktop application includes a preference that disables red-lettering, but the iPhone application has no option, and you're forced to abide it. It seems to me that the setting certainly ought to be there—there are those who find red-lettering distracting, or who feel as if it perpetuates a sense that somehow some words in Scripture are less authoritative than others.
Perhaps this isn't the right forum for such a suggestion or critique, so if this topic would fit elsewhere, and therefore be for effective, I hope a moderator will be kind enough to move it.