Still problems with the editor custom theme

Hi guys,
I’m creating some new newsletter and it seems that I still have the problem with the editor and a problem with the custom theme.

1. Editor problem
In the editor I create a brand new text.
I didn’t change any color at all. So it should be all the same color.
In fact in the editor everything seems to work right:

editor screenshot

But then when I receive the newsletter it looks like this:

newsletter screenshot

here the difference is subtle, but you can see that the first paragraph is black and the second paragraph is grey.
I have this changes in the all newsletter. Sometimes instead of the black I get the font in purple.
The code of the page is correct (i can give you the html if needed), so there isn’t a wrong setting in the code.

What can I do to solve this issue?

2. Custom Theme Problem
I followed the instractions to make a custom theme and it worked. Now I wanted to change the h3 color. I tried to change it in the editor but it didn’t work.
I tried to edit the css file in the theme folder, but it didn’t work (in the file I have the color that I want, but in the editor it doesnèt appear).

I tried to unistall the theme and reinstall with the new css but still nothing.
In the gmail I can see the html code and at one point I have this:

text-align:left;
    }h3 {
        color:#47403f !important;
        display:block;
        font-family:Arial;
        font-size:26px;
        font-style:normal;
        font-weight:normal;
        line-height:125%;
        letter-spacing:normal;
        margin:0;

the color shouldn’t be #47403f, but #fbad18 as in the css file.

Where is it taking this setting?

Please tell me if you need something more, as the css file, html newsletter or anything.
Thank you very much.

https://wordpress.org/plugins/wysija-newsletters/