The conversion is exact
Hex is RGB. #FF5733 is literally FF, 57, 33 read as three base-16 numbers
— 255, 87, 51. Nothing is approximated and nothing is lost, in either direction.
That is worth knowing because it is not true of every pair on this site: HSL and CMYK both round, and hex to RGB does not.
Where you need the channels
rgba()when you want the same colour at partial opacity — hex alpha exists but is still awkward in older tooling.- Canvas and image work, where pixels are three numbers.
- Anywhere you need to compute: mixing, contrast, or a lightness check all need the channels, not the string.
Shorthand and alpha
#f53 expands to #FF5533 — each digit doubles, which is why only some colours
have a three-digit form. An eight-digit #FF573380 is read and the alpha
dropped, because rgb() here carries three channels, not four.
Questions
Is anything lost?+
No. Hex and RGB are the same numbers in different bases, so the conversion is exact in both directions — unlike HSL or CMYK, which round.
What about #f53?+
Three-digit shorthand expands by doubling each digit: `#f53` is `#FF5533`. Only colours whose pairs happen to match can be written that way.
Can I get rgba() out of this?+
The alpha in an eight-digit hex is read and dropped, because the other notations here do not carry it. Keep opacity as a separate value.