editor.kv

<YourWidget>:
    canvas.before:
        Color:
            rgb: self.variable_color
        Rectangle:
            pos: self.pos
            size: self.size

<MyScrollView>:
    canvas:
        Color:
            rgb: 1, 1, 1
        Rectangle:
            pos: self.pos
            size: self.size

<MyGridLayout>:
    canvas:
        Color:
            rgb: 1, 1, 1
        Rectangle:
            pos: self.pos
            size: self.size

labelP.py

from kivy.uix.widget import Widget
from kivy.uix.gridlayout import GridLayout
from kivy.uix.scrollview import ScrollView
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.tabbedpanel import TabbedPanel, TabbedPanelHeader
from kivy.core.window import Window
from kivy.properties import ListProperty
from kivy.app import App


class YourWidget(Label):
    variable_color = ListProperty((1, 1, 1))

    def __init__(self, **kwargs):
        super(YourWidget, self).__init__(**kwargs)
            #Label.halign="left"

    def on_touch_down(self, touch):
        if touch.y > self.y and touch.y < self.y + self.height:
            if self.variable_color == [1, 1, 1]:
                self.variable_color = (0, 0, 1)
        else:
            self.variable_color = (1, 1, 1)


class MyScrollView(ScrollView):
    pass


class MyGridLayout(GridLayout):
    pass


class pathways(Widget):
    def __init__(self, **kwargs):
        super(pathways, self).__init__(**kwargs)
        self.layoutMain = MyGridLayout(cols=1, spacing=1, size_hint=(None, None), width=400)
        self.layoutMain.bind(minimum_height=self.layoutMain.setter('height'))

        self.layoutChose = MyGridLayout(cols=1, spacing=1, size_hint=(None, None), width=400)
        self.layoutChose.bind(minimum_height=self.layoutChose.setter('height'))

        for i in range(30):
            btn = YourWidget(text='[color=000000]' + str(i) + 'Hello World[/color]', markup=True, size=(400, 20), size_hint=(None, None))
            # the next line fix the alignement
            btn.bind(texture_size=btn.setter('size'))
            self.layoutMain.add_widget(btn)

        self.troot = MyScrollView(size_hint=(None, None))
        self.troot.size = (400, 320)
        self.troot.center = 300, Window.height - 300
        self.troot.add_widget(self.layoutMain)

        self.troot2 = MyScrollView(size_hint=(None, None))
        self.troot2.size = (400, 320)
        self.troot2.center = 750, Window.height - 300
        self.troot2.add_widget(self.layoutChose)

        self.add_widget(self.troot2)
        self.add_widget(self.troot)

        self.layoutMain.bind(on_touch_up=self.moveChild)
        self.layoutChose.bind(on_touch_up=self.moveChild)

    def moveChild(self, touch, *l):
        T = []
        for childF in self.layoutChose.children[:]:
            if childF.variable_color == [0, 0, 1]:
                T.append(childF.text)
            self.layoutChose.remove_widget(childF)

        for childT in self.layoutMain.children[:]:
            if childT.text in T:
                childT.variable_color = [1, 1, 1]

            if childT.variable_color == [0, 0, 1]:
                btn = YourWidget(text=childT.text, markup=True, size=(400, 20), size_hint=(None, None))
                self.layoutChose.add_widget(btn)


class Editor(App):
    def build(self):
        tp = TabbedPanel()
        tp.default_tab_text = 'Files Setup'
        tp.default_tab.content = Button(text="Just a button")

        th1 = TabbedPanelHeader(text='Organisms')
        tp.add_widget(th1)

        pathways()
        #Listtt2 = pathways()
        th1.content = pathways()

        return tp


if __name__ == '__main__':
    Editor().run()