javascript - How can i remove the span which created by method document.execCommand()? -

the html code

<p contenteditable="true" onmouseup="setcolor();">this text</p> 

and javascript code

document.execcommand('stylewithcss', false, true); document.execcommand('forecolor', false, "rgba(0,0,0,0.5)") 

; dom tree becomes：

<p contenteditable="true" onmouseup="setcolor();">     <span style="color: rgba(0, 0, 0, 0.498039);">some</span> text </p> 

noticed inserts span label,with style attribute,the word's color changed. should ,when want remove span label?so word's color turn default back.i've tried

document.execcommand('forecolor', false, ""); 

but doen't work. thank much!