Of Arietta colour conundrums

As has been made apparent (although perhaps not officially announced), I am participating in Nakniswemo. (As with the "National Latin Exam" and "National Mythology Exam" - they somehow become "(inter)National".)

I am knitting Arietta, which was probablly a bad choice as its knit on 2.75 and 3.25mm needles with 4 ply. That's going to be way more than the suggested 50,000 stitches. However, I persist. I have cast on, and although I've fallen behind my own daily goal of 30 rows of back (or 60 rows of a front piece or sleeve), I have made a little progress.



However, I'm having some issues with the colours. I had originally wanted to use the colours and yarn from the pattern - as part of the reason I liked the cardigan was the colour combo. I'd even managed to get over the hurdle that Knit Picks wouldn't ship to Australia (thanks to Adina).

However, it would appear that now Knit Picks no longer stocked the colours of the yarn I wanted, so I decided rather than have to pay heaps for postage and place a burden on Adina, that I would just try to buy similar colours here. I decided to go with Heirloom Cotton 4ply. I picked colours that looked similar to the ones used and this is what I came up with. (N.B. I subed blue for the slate colour as the pattern notes that in this pattern it looks a bluey colour, which is something I liked.)



But here is my problem - the beige on the left looks almost the same as the cream on the right; the beige isn't dark enough. This wouldn't be a problem except that a few rows up the chart from where I am those two colours sit next to each other for about 6 rows. Ideally I should use a darker brown/beige but the only one in Heirloom is the dark brown I'm already using and I'd rather not rip it back. Do you think there is something I could substitute it for instead? (A violet? A yellow? A white - just for a tiny bit more contrast? A ?????) (Help!!!!!!!)

[I realised I may have screwed up the colour combo even more, when looking for a tip on the decreases and the chart, looked at people's posts about Arietta on Ravelry. I totally haven't thought about warm/cool colours or anything - any project saving advice much appreciated - especially something telling me I don't have to rip it back - I can just change the cream - I feel too committed now - it doesn't look that far but it so is.]