HEX, RGB and HSL color codes explained
HEX and RGB describe red, green and blue channels. HSL describes hue, saturation and lightness. The picker converts between them for the same sRGB color.
Use the code your tool expects
In a six-digit HEX code, the first two digits give red, the next two green and the last two blue. For #0B7285 those channel values are 11, 114 and 133, so the RGB form is rgb(11, 114, 133).
An eight-digit HEX code adds an alpha channel. The visible result of transparency depends on the background; compare colors against the background you will actually use.
Use a wheel to change hue
Hue wraps around a circle. Saturation and lightness let you change the color without choosing a different point around that circle. At zero saturation, changing hue leaves the same gray.
The wheel uses the same sRGB HSL conversion as the picker. Its complementary mode compares hues 180 degrees apart; triadic compares hues at 0, 120 and 240 degrees from the selected hue. These relationships do not guarantee readable text contrast.
Screen color is not a print proof
These tools work with sRGB values. A screen preview cannot establish how a particular ink and paper combination will print. For text on a screen, send the actual foreground and background values to the contrast checker.