colors for different fields

Are you referring to the labels for each field? If you are, then yes you could.

Each label has its own unique ID so you would simply need to inject custom CSS code to specify the color you want for each.

For example, if I inject the ff css code

For Label

#label_3{color:#2FE01B;}

#label_5{color:#221BE0;}

For the actual text box

#first_3{background-color:#2FE01B;}

#last_3{background-color:#221BE0;}

This will be the result

Are you able to provide me with the link to your form?

That way I can help you identify the ID for each label and then I'll walk you through the process of injecting custom CSS code.

Thank you for the link. May I ask which part of that specifically would you like to change the color?

Alright. I cloned your form and edited the color of "Referral Source". Its ID is label_40, so this is the CSS code I injected: 

#label_40 {color:#4EA8F2;}

and this is the result

To identify the ID of each element of the form, whether it be the label or the textbox or button, etc simply right-click and then click on View Source.

This is how I found out that the ID for "Referral Source" in the sample above is label_40

 

If you'd like to know how to inject custom CSS code, this is a very helpful tutorial

http://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes