Usability for notification messages, colors [web apps]

In each web app I develop, I like to add three types of messages:

• Green/blue for success messages
• Yellow for warnings
• Red for errors

And perhaps, a neutral one for i开发者_如何学编程nformation, which is gray or blue if the success one is green.

The success one is used for when an item is created or updated, the yellow one is when there's something wrong, but not we-are-going-to-die wrong and the red one is when something is blocked or we are going to die.

However, there's one thing I can't figure out, when I delete an object, what kind of notification should I use? I think the success one is not because it is not expected, altough the deletion was successful, the user tends not to read the message, just to see the color.

The red one might be, but it can be misunderstood (I tried to delete it but there was an error), the warning and the information one might be good choices, but I'm not really sure.

Also, when you ask for confirmation about deleting something, the 'cancel' button should be green or red?

I'm just curious how you guys handle this. Thanks.

In general, I rely on the OS to provide appropriate colors.

The problem is with vision-impaired users. I can't predict whether or not they can read text set against any background I might choose. I assume that they've configured their browser and OS to display the colors that they can read the best.

Mike brings up a good point. Using colors assumes the user can see colors. Perhaps adding an icon (with contrasting foreground and background colors) to your messages may help with the ambiguousness.

For example:
Exclamation: Exclamation point in a triangle with a yellow background.
Asterisk: Lowercase letter i in a talk bubble.
Stop: White X in a circle with a red background.
Error: White X in a circle with a red background.
Warning: Exclamation point in a triangle with a yellow background.
Information: Lowercase letter i in a comic bubble.
Question: Blue question mark in a talk bubble.

I usually do it the following way:

If the user's intention was to delete something, and he did, I show it in green. If they don't read it because its green, they will assume that whatever they wanted to do has been done correctly.

At the "are you sure?" stage, the user may have gotten there by accident, so if you give a color, he may get confused or scared. I keep the "delete/cancel" buttons in a neutral color.