Identify the rule and find the missing number

The following sets of numbers are connected through a common rule/patern. Find the missing number(?)

$$(255,153,51x)(153,0xx,51x) = 669900$$

$$(255,204,51x)(204,51x,51x) = 339900$$

$$(153,153,204)(0xx,204,51x) = ?$$

• The $0x$ on the first row, is it intentional or should be $0xx$? Then on the last row, the second number in each triplet, shouldn't they be swapped? May 15 '19 at 0:36
• Yeah you are right about the x. But no, the numbers dont need to be swapped. May 15 '19 at 0:38
• Did you intentionally remove the first x (from 51x between first brackets)?
– Imus
May 15 '19 at 13:40

My guess is

$$993399$$

Because

We need to calculate the difference between the triplets, so we have:

$$(255,153,51x) - (153,0xx,51x) = (102,153,0xx)$$
$$(255,204,51x) - (204,51x,51x) = (51x,153,0xx)$$
$$(153,153,204) - (0xx,204,51x) = (153,51x,153)$$

Then

Ignoring $$x$$, translate each number into hex (base-$$16$$), so we get:
$$(102,153,0) = (66,99,00)$$
$$(51,153,0) = (33,99,00)$$
$$(153,51,153) = (99,33,99)$$