Tklib tooltip usage problem with configure

I have added tooltips to some widgets and they work fine. For example:

package require tooltip

...
    tooltip::tooltip $panel.optionsButton "Modal Show/Hide"

But the tooltips come with a sort of blue/grey background whereas I prefer
the more traditional light yellow.

So I tried this:

tooltip::tooltip configure -background yellow and got this:

Error in startup script: invalid command name ".__tooltip__.label"
    while executing
"$b.label configure $opt"
    (procedure "configure" line 13)
    invoked from within
"configure {*}$args"
    (procedure "tooltip::tooltip" line 34)
    invoked from within
"tooltip::tooltip configure -background yellow"
    (procedure "test::make" line 11)
    invoked from within
...

It is no different if I use ::tooltip::tooltip. And I get a similar error
if I just try to print the config options, e.g.,

puts [tooltip::tooltip configure]