Of the MSDS that I have seen for gels and gel polishes containing the cat-eye effect, the ingredient that appears to be used to create this effect is Iron Powder which is suspended in the gel. The magnet attracts this powder to create this effect (like the experiment we all did in school where we used a magnet under a paper that had loose iron filings.
EC Directive 1223/2009, APPENDIX IV "LIST OF COLORANTS ALLOWED IN COSMETIC PRODUCTS" lists all the colourants that are allowed in cosmetics. Iron Powder is not included in this list and therefore not permitted.
But to double check, I contacted CVUA which is the authority in Germany responsible for cosmetic safety:
“To your question about iron powder. If it is used as a colourant, it is not authorised, because iron powder is not listed in the Annex.”
If canni-uk has any fact-based information to support his argument that cat-eye gels or GP are legal, I'd be grateful to receive it.