@cishore I don't think there's is an "easy" way to modify the file if you do it like in this tutorial. But I can give you tips on how to do what you aim for.
If you don't have many trucks, it should be easy to find the truck in question. Although, if you have a lot of trucks, you may want to make sure you're driving the truck you want to modify, for easier reference. Then you can search for "my_truck: " and there's only one occurrence conveniently. You'll need to search for that address until you'll see "vehicle : " followed by the address. Optionally, you can copy the address and paste it in a new notepad document.
Next part requires a little bit of search, since you'll want to scroll down and find the paint job of your DAF. You can look for clues, like if nearby parts has reference to "daf.xf", or search for the address of the paint job, which should bring you back to the list of accessories. Then you can look further above for the vehicle address and see if it matches the one pasted in the new notepad document.
For the actual paint job, it'll be a little bit tricky to have custom colors without the right tools, since you probably won't go too far with something that looks like this: "&3f7b74cd". That's the way SCS decided to save the color values. I'm going to guess the darker shade of gray on that paint job might be one of those mask color (I'm not sure why SCS made it _r, _g, and _b since they're just color 2, 3 and 4, while 1 is base color). When it's unused, you'll usually see something like (1, 0, 0), (0, 1, 0), or (0, 0, 1) with commas in between, but not always the case. Since you want the second color to be red (really simply color), I think the quickest way would be to put the first three mask colors as (1, 0, 0), so you'll be guaranteed to get the result you want. If you want a different shade of red, you might need to use a tool for that, there should be a link for it in the tutorial.