How to remove ":" (colon) when displaying field name?
Note: The OP is not talking about Views. (In Views you can uncheck a box that says Place a colon after the label).

The accepted Drupal method is by copying the core field.tpl.php file into your theme directory and manually removing the colon from the file.

modules/field/theme/field.tpl.php
sites/all/themes/[mytheme]/field.tpl.php


In Drupal 7 this is on line 55:

from:

&lt;div class="field-label"&lt;?php print $title_attributes; ?&gt;&gt;&lt;?php print $label ?&gt;:&amp;nbsp;&lt;/div&gt;


to:

&lt;div class="field-label"&lt;?php print $title_attributes; ?&gt;&gt;&lt;?php print $label ?&gt;&amp;nbsp;&lt;/div&gt;


In order to do this in a specific content type you first copy field.tpl.php to your theme, then duplicate it, adding the machine name of your content type, and remove the colon from the content type specific version.

sites/all/themes/[mytheme]/field.tpl.php
sites/all/themes/[mytheme]/field--[content-type].tpl.php


Note: the double hyphen (--) is not a typ-oh.

Read up on theme suggestions for more. Using suggestions you can target just a specific field in this content type, just the field globally, all fields in the content type, or all fields in all content types. Or handle every combination differently.