I hadn't run into this problem yet, but it definitely would be worthwhile to have more flexibility on changing label color.  If no one has a work around, I would suggest putting this up in the Ideas section if it isn't already there.

Hi Joan,

This link may help ful to you

http://kb.tableausoftware.com/articles/knowledgebase/Mark-Labels

I am struggling with this, as well. After several years of using Tableau, this is the first time I have had this issue, which makes me wonder if it is a recent bug. Anyone else have a fix for this?

This article does not provide a solution to the posted problem.

Did some more searching, and the only reasonable suggestion was to use a dual axis and overlay two charts, then change the font color for one to white and the other to black.

I ran into the same problem when I changed the font size of a label.

I lost the contrast color when I increased the font size,

but then when I increased the size of the underlying square,

the contrast colors returned.

It may be possible that your new font is larger than Arial, and perhaps decreasing your font size

or increasing your bar size may return the contrast colors.

I lost smart color feature as soon as I re-assigned the color on the worksheet. Changing it back to the original color did not help, but then I noticed the "clear" button way down on the format panel, and it re-set the defaults. I believe, any font changes, such as size, bolding, font name, will not remove the smart color feature, as long as you don't change the color. Once you did - use the clear button.

@swaroop.gantela

This technique worked. Thank you!

I had similar issue, I just had to go to the Label mark card and click it, then Uncheck "Allow labels to overlap othermarks"

Anna - thank you for the "Clear" technique!  I've been struggling with this for months and now have a solution! 

I believe I have the issue the OP have see screenshot:

On the Labels card, there is the font option.

By clicking on the black box it changes the text to black if the bar is orange or if the bar is blue

Click the Automatic button to go back to the white text in the blue box.

Kind regards,

Stephen

Apparently only if you are using Arial. Not if you are using another font. It used to work in other fonts. Seems to be a new "feature".

This was the answer for me. Clear did nothing, but switching fonts from Tableau Book to Arial immediately gave me the smart colors.

Thanks, resizing the bars solved the problem for most labels, but for the very smallest bars, where the label barely exceeds the bar size, the color changes to black. I would like to have control over how the auto-coloring works, so as to force white color in these cases. I understand that the background color affects the color choice here, but in order the make the color flip back, the backgound has to be really dark, much too dark.

Moving the labels outside does not look as good either when the reference lines cross the labels.

There is an idea relating to this issue:

Smarter Auto-Labelling