When you compose an email, you will use the default font style. If you do not like the default text style such as the font color, the font size, etc in Gmail, you can change it in the settings section.
Step 1: Login your Gmail account (please refer here to open one if you do not have an account yet);
Step 2: In the Gmail account, click the "Setting" button from the right-top corner;
Step 3: Click the "Settings" command from the drop-down list;
Step 4: Click the "General" tab in the settings menu;
Step 5: Scroll the cursor down and select the font, the font size, and the font color in the "Default text style" section;
Step 6: Click the "Save Changes" button at the bottom;
Step 7: When you compose an email next time, you will see the text you type is different;
Step 8: To remove the changed text style and return to the default style, click the "Remove formatting" in step 5 and save the changes.