Several people have mentioned that my colors look good together and they have problems choosing what colors to use.   I have some practice with this due to making designs for my online stores.   There is a thing called Color Theory and while that gives an idea of how colors go together, I still maintain that you can't do anything wrong when coloring.   For other areas of life, there are probably color combos that you want to stay away from, but in coloring the sky's the limit.

Essentially color theory is putting colors in a logical order next to each other.   This is most often accomplished with a color wheel.   There are 3 types of colors:  primary, secondary and tertiary.  

Primary colors are colors that can't be made by mixing other colors together.  The primary colors are blue, red and yellow. 

Secondary colors are colors made by mixing the primary colors together.  The secondary colors are purple (red/blue), green (blue/yellow) and orange (red/yellow).

Tertiary  colors are colors made by mixing a primary color and a secondary color.  They have 2 names as a result, for example yellow-orange.

There are also shades and tints, but I don't want to get too complex in this post.  Quick and dirty version:  shades are a color plus black and tints are a color plus white.

Colors that are opposite each other on the wheel are called complementary and colors next to each other are called analogous.  Colors on the top half of the wheel are considered warm and the bottom half is considered cool colors.

There are as many ways to combine colors are they are opinions      You can use all warm colors or all cool colors.  You can use complementary colors or analogous colors.  You can use warm colors with cool color accents or cool colors with warm color accents.  

Things you may want to avoid are an entire picture that is "too harmonious."   If you do an entire picture in reds there may not be enough contrast and it will look boring.   If you use too many wildly different colors it may be too chaotic and overwhelming.

When I am coloring a page, I try to kind of split it into areas in my head and try to get an idea of what I want for the overall look.  If I have a picture with a lot of leaves, I will make the leaves with several different greens rather than a whole wall of green.  If I have a bunch of flowers, I will try to use bright colors and then use a darker shade on other parts so it's not too blinding, as flowers are generally relatively small in the pages I do.

As I said in a comment, you really can't do anything wrong when coloring.   Pick what looks good to you and just have fun with it.  The more you color the easier it will be to pick your color.  You will probably gravitate toward certain colors a lot of the time, which is normal.   So stop worrying and start coloring!

Additional Reading:

http://www.worqx.com/color/

http://www.colormatters.com/color-and-design/basic-color-theory

https://en.wikipedia.org/wiki/Color_theory