.el-form-item__label{
color: red;
}
<el-form-item label="年龄" prop="age" class="item">
.item .el-form-item__label{
color: red;
}
<el-form-item>
<span slot="label">label 值 <span class="red">(特殊提示)</span> </span> // slot
<el-input></el-input>
</el-form-item>