Importing using Hex and exporting using RGB255 does not always return the correct values

[belak]

Ran into an example with the base16-builder-go where grabbing a value from a hex string and then outputting the rgb values then converting them back to hex isn't matching up.

Here's an example:

package main

import (
	"fmt"

	"github.com/lucasb-eyer/go-colorful"
)

func main() {
	color, _ := colorful.Hex("#4a4543")
	r, g, b := color.RGB255()
	fmt.Printf("#%02x%02x%02x\n", r, g, b)
}

As you can see the input value is #4a4543 but (on my machine) it outputs #494543.

[belak]

It looks like the fix is fairly simple (add 0.5 to all the values from RGB255 before converting to uint8, same as what Hex does), but the tests are painful because they don't line up with the other values (turns out using numbers that aren't as clean for input means you don't get numbers as clean in the output ☹️ ) and there are no tests covering RGBA or RGB255.

[belak]

Also, as far as I can tell, this is related to golang/go#20100 as well because even the +0.5 isn't a perfect round function.