ΔE 20.9, loose: different enough that you should pick on purpose. Royal Blue is a little lighter, much more saturated than Turquoise Deep.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Royal Blue is a little lighter, much more saturated than Turquoise Deep.
The same difference applies the other way round: Turquoise Deep is a little darker, much more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Turquoise Deep on the colour wheel See Royal Blue on the colour wheel
All matches: Turquoise Deep equivalents · Royal Blue equivalents