For this tutorial, you will need this hexadecimal color combiner tool. It makes breeding SO much easier, and is completely accurate (though some SLIGHT variation in color may occur due to wajas' coding).
http://www.colortools.net/color_combination.html

How To Use The Hexadecimal Color Tool To Predict Pups:

This is is what you will see when you open the hexadecimal color combiner tool.
For our wajas project you will only need to worry about 4 things; color 1, color 2, combine (button), and combined (color). Don't worry about the websafe color box, as it's not important.

These my two blue rose tempests, Delphinidin (left) and Majahal (right) who will be our test subjects. I choose all of my custom's colors specifically for what colors they make when combined. (I will explain more on that later). Take note of each hexadecimal color.

Base Color: 000000 Eye Color: 5151FF Leg Spots: 5151FF Wind: 669829 Merle: 5151FF

Base Color: 000000 Eye Color: 6EA6FF Leg Spots: 6EA6FF Wind: 669829 Merle: 6EA6FF

The next thing you would need to do, is to open up the wajas Custom Demo page. Duplicate your parent wajas' breed & markings in the drop down boxes.

For this test your Demo should look something like this:

For a good example on how to combine color, we will use the color of the merle on each waja.

Pull your color combiner back up. Put one waja's color in the "Color 1" box, and the mate's color in the "Color 2" box. Then press combine, and EUREKA! You have the mixed color in the "Combined" box! In this case we would have Delphinidin's 5151FF + Majahal's 6EA6FF. 5151FF + 6EA6FF = 607CFF!

So how do you use this information to predict what pups will look like? Take each color from each parent, combine them, and place them in the Custom Demo boxes accordingly. Then press, generate! And POOF you have a prediction of what your pup would look like!

For Delphinidin x Majahal the results would look something like this:

NOTE: This only perfectly works if your wajas have strong markings! (say 70-100%) Markings with less than 100% will have accurate coloring, but will appear faded. I will discuss this more momentarily.

A lot of people open photoshop, or paintshop, and combine the parent's layers to predict how pups will look, but I just don't find that accurate.

So how accurate is this test? The best I have found yet! See for yourself!

Actual Majahal x Delphinidin pup: