Hello,

Which one forecolor that you referred to? We have several forecolor style in WebCombo such as TextBoxStyle,FrameStyle,ResultBoxStyle and etc.
I think you could not change the style via properties in javascript. You only can change it via element.
For tooltip, currently, there is no method to change its tooltip. You also could not set it via properties in javascript. However, you can get the div text element and set the title.
E.g Please refer into my sample.

Regards,
Handy

I want to change the TextBoxStyle's forecolor. I use GetControlElement() to get the element,but it still doesn't work

Hello,

You will need to use GetFrameElement(). 

e.g             combo.GetFrameElement().childNodes[2].childNodes[0].style.color = "Red";

When you set from element, you only set for normal mode. You need to validate so it can work such as in 3 modes.

Regards,
Handy