Earth Warp/Crossing the river

At the start of the challenge, the text of "Ollie and the children make their way to the probe. 'Now all I have to do is slip in my mark two flidget to turn the probe off.' says Ollie. 'Oh, no!' yells Ollie, 'It doesn't fit! I will need a mark three flidget! I'll have to call Gia for a spare.'" shall appear on the screen; once you have pressed Space to continue the text "'Has anyone seen my orb?' asks Ollie. 'It looks like a round, shiny ball! I will need to fit it into my ship's communicator so I can call home.'" will appear on the screen. Once you have pressed Space again, the text "But nobody knew where the orb was. 'I think I must have dropped it on the other side of the river,' moans Ollie." shall appear below it - and once you have pushed Space for a third time, an overhead view of the river with sixty-two randomly-coloured rocks in it will appear on the screen with the text of "'I have left a trail of stones to show you the way across.' Says Ollie." below it. Once you have pushed Space for a fourth time the text of "You have to get to the far side, but each stone may only be used once." will appear on the screen; once you have pressed Space for a fifth time, a plus sign indicating the children's current position will appear on the first rock of the river's near side, flash three times, and leave a right-pointing arrow behind as it moves to each of the next seven rocks in turn as the text "Use the arrow keys to hop to another rock. Carry on the pattern of colours." appears on the screen (the "pattern of colours" is shown in the first eight rocks). If you press the left, down or right arrow keys at this point, Ollie will say from off-screen "Start by moving forward.", and you'll have to press Space to continue - and once you have pressed the up arrow key, the plus sign will move to the ninth rock in the sixth row and leave an up-pointing arrow behind, as the text "Use the arrow keys to hop to another rock. Tap S if you want to start again." appears on the screen. If you press the down or right arrow keys at this point, Ollie shall say from off-screen "You can't go that way!" (he will also say this if you push the down arrow key while the children are on any other rock in the sixth row, if you push the left one while they are on the first rock of any row, and if you push the right one while they are on the ninth rock of any other row), and you'll have to press Space to continue; also, if you should try to move back to a rock you've already stepped on (indicated by an arrow pointing in the direction that the children moved off it), Ollie will remind you from off-screen: "You may only step onto each rock once.", and you shall have to press Space to continue. If you get stuck, you can either press S to return time back to when the children were on the eighth rock of the river's near side, or intentionally move onto a rock of the wrong colour (in which case, Ollie shall say from off-screen "Oh dear! You've fallen in the river. You needed a blue/green/red rock!" and you shall have to press Space to restart the challenge) - however, once you have reached the far side of the river, the text "Well done! You got safely across the river." will appear on the screen and you'll have to press Space for a minimum sixth time to go on to the fifth challenge (which is similar to the eleventh one of Sky Hunter but has added symmetrical-pattern puzzles).