gistfile1.vim

fun! s:use_eval(co)
    let c = a:co
    let r = eval('0x'.c[0].c[1])
    let g = eval('0x'.c[2].c[3])
    let b = eval('0x'.c[4].c[5])
    return [r,g,b]
endfunction
 
fun! s:without_eval(co)
    let c = a:co
    let r = str2nr(c[0:1],16)
    let g = str2nr(c[2:3],16)
    let b = str2nr(c[4:],16)
    return [r,g,b]
endf
 
function! s:nr2hex(nr)
    let n = a:nr
    let r = ""
    while n
        let r = '0123456789ABCDEF'[n % 16] . r
        let n = n / 16
    endwhile
    return r
endfunction
let start = reltime()
for i in range(0x100)
    " let color = ( '000000'.s:nr2hex(i) )[-6:]
    let color = repeat( ('00'.s:nr2hex(i))[-2:], 3 )
    let l1 = s:use_eval(color)
    let l2 = s:without_eval(color)
    if l1 != l2
        echo "Failed at: ".i
    endif
endfor
echo "time cost".reltimestr(reltime(start))
echo "All pasted!"

gistfile2.vim

let color = '012345'
let times = 1000
echo "Results:"
echo "-----------------------------------------"
echo "run: ".times." times"


fun! s:use_eval(co)
    let c = a:co
    let r = eval('0x'.c[0].c[1])
    let g = eval('0x'.c[2].c[3])
    let b = eval('0x'.c[4].c[5])
    return [r,g,b]
endfunction

fun! s:without_eval(co)
    let c = a:co
    let r = str2nr(c[0:1],16)
    let g = str2nr(c[2:3],16)
    let b = str2nr(c[4:],16)
    return [r,g,b]
endf


let start = reltime()
for i in range(times)
    call s:use_eval(color)
endfor
echo 'use eval:'.reltimestr(reltime(start))

let start = reltime()
for i in range(times)
    call s:without_eval(color)
endfor
echo 'without eval:'.reltimestr(reltime(start))

gistfile3.txt

Results:
-----------------------------------------
run: 1000 times
use eval:  0.022386
without eval:  0.019251