Go to the Text Editor in Blender, press the plus ("+") button to create a new text object, paste the code below and press "Run Script". Then on the 3D View, press SPACE and type "random theme operator" and ENTER to use it.

Random Theme Operator.py

import bpy
import blf
import bgl
import random


def drawCallback(self):
    blf.size(0, 16, 72)
    text = ('Last changed: ' + self.currentPropName) if self.currentPropName else 'Press LEFT or RIGHT to change color, ESC to stop'

    blf.enable(0, blf.SHADOW)
    blf.shadow(0, 3, 0.0, 0.0, 0.0, 1.0)
    blf.shadow_offset(0, 2, -2)

    bgl.glColor3f(1.0, 1.0, 1.0)
    blf.position(0, 40, 40, 0)
    blf.draw(0, '(Press ESC to stop)')
    blf.position(0, 40, 70, 0)
    blf.draw(0, text)
    
    blf.disable(0, blf.SHADOW)
    


class RandomThemeOperator(bpy.types.Operator):
    bl_idname = "wm.random_theme_operator"
    bl_label = "Random Theme Operator"
    bl_options = {'REGISTER'}    


    def getColorProps(self, colorsList, prop, propName, parentName=''):
        for subProp in prop.rna_type.properties:
            if subProp.identifier in {'rna_type', 'srna', 'fixed_type'}: # Ignore some properties.
                continue
                      
            if hasattr(subProp, 'type'):
                if subProp.type == 'POINTER':
                    self.getColorProps(colorsList, getattr(prop, subProp.identifier), subProp.name, parentName if parentName else prop.name)
                elif subProp.subtype == 'COLOR_GAMMA' or subProp.subtype == 'COLOR':
                    colorsList.append(
                        (prop, subProp.identifier, parentName + ' ' + propName + ' ' + subProp.identifier)
                    )
            else:
                self.getColorProps(colorsList, getattr(prop, subProp.identifier), subProp.name, parentName if parentName else prop.name)
        return colorsList
    
    
    def updateColor(self, r, g, b):
        prop, attr, name = self.allColorsList[self.index]
        setattr(prop, attr, (r, g, b, 1.0) if len(getattr(prop, attr)) == 4 else (r, g, b))
        self.currentPropName = name


    def modal(self, context, event):
        context.area.tag_redraw()
        
        if event.type in {'LEFTMOUSE', 'RIGHTMOUSE', 'ESC'}:
            bpy.types.SpaceView3D.draw_handler_remove(self._handle, 'WINDOW')
            bpy.ops.ui.reset_default_theme()
            self.report({'INFO'}, 'Cancelled')
            return {'CANCELLED'}

        if event.type == 'RIGHT_ARROW' and event.value == 'PRESS':
            r, g, b = 0.1, 0.3, 0.7
            if self.lastDirection == 0:
                self.updateColor(r, g, b)
            self.index = min(self.index + 1, self.maxLimit)
            self.updateColor(r, g, b)
            self.lastDirection = 1

        elif event.type == 'LEFT_ARROW' and event.value == 'PRESS':
            r, g, b = 0.7, 0.5, 0.0
            if self.lastDirection == 1:
                self.updateColor(r, g, b)
            self.index = max(self.index - 1, 0)
            self.updateColor(r, g, b)
            self.lastDirection = 0
            
        return {'RUNNING_MODAL'}


    def execute(self, context):
        self.index = 0
        theme = context.user_preferences.themes[0]
        self.allColorsList = tuple(reversed(self.getColorProps([ ], theme, theme.name)))
        self.currentPropName = ''
        self.maxLimit = len(self.allColorsList)-1
        self.lastDirection = 1

        self._handle = bpy.types.SpaceView3D.draw_handler_add(drawCallback, (self,), 'WINDOW', 'POST_PIXEL')
        context.window_manager.modal_handler_add(self)
        context.area.tag_redraw()
        return {'RUNNING_MODAL'}


def register():
    bpy.utils.register_class(RandomThemeOperator)


def unregister():
    bpy.utils.unregister_class(RandomThemeOperator)


if __name__ == "__main__":
    register()
    
    # Go to the 3D View, press SPACE and type "random theme operator".
    # Then hold the RIGHT ARROW key.