Blue Burst

#309cd0

A blue that is muted. It is light — black text sits on it comfortably, white text does not.

Hex

#309cd0

RGB

48, 156, 208

OKLCh

65.6% 0.122 234.5°

CIELAB (D50)

60.2, -17.7, -36.0

What is true of this colour, and of no other

6 other named colours sit within ΔE00 2 of it.
It uses 88% of the chroma sRGB can show at this lightness and hue — close enough to the boundary that a wider display would show it slightly more vividly.
As text on white it measures APCA Lc 57.5; on black, Lc -44.3. The sign is the polarity, which the WCAG ratio discards.
Built into an eleven-step scale, 10 of the 10 adjacent pairs stay ΔE00 2 apart — see the ramp.
protanopia and deuteranopia and tritanopia shift it by ΔE00 21.4 and 20.7 and 20.3 — no red cone.

Text on this colour

White text

3.09:1 — large text only

Black text

6.79:1 — passes AA

Black text is the better of the two at6.79:1. That is enough for body text.

As text on white, it needs to change

#007fb0 is the nearest colour of the same hue that passes AA on white, at 4.50:1. Only the lightness moved, and some saturation was given up to stay inside sRGB.

Try it against your own background

The same colour, with one cone missing

As you see it

#309cd0

protanopia

#9595d0 · ΔE00 21.4

deuteranopia

#8787d1 · ΔE00 20.7

tritanopia

#7777ff · ΔE00 20.3

Run a whole palette through all three

The twelve nearest named colours

Ranked by CIEDE2000 — perceptual distance, not hex arithmetic. The closest isStructural Blue at ΔE00 1.307: between 1 and 2 — a trained eye spots it when the two touch; nobody spots it across a room. What the numbers mean.

Structural BlueΔE00 1.307 · #0e9bd1
Stratos BlueΔE00 1.377 · #3799c8
SorcererΔE00 1.503 · #3398ce
BlitheΔE00 1.75 · #0099d1
Blue DamselflyΔE00 1.859 · #2fa1da
Blessed BlueΔE00 1.959 · #4499cc
Peaceful RiverΔE00 2.063 · #47a0d2
Tomb BlueΔE00 2.137 · #0099cc
Bayern BlueΔE00 2.187 · #0098d4
Astrolabe ReefΔE00 2.213 · #2d96ce
DayflowerΔE00 2.284 · #38a1db
Isle of CapriΔE00 2.659 · #0099c9

12 of these have no page of their own: pages exist for the 4,961 colours the dataset marks as good names.