For an applicant failing the Ishihara test, the next step is a medical assessor. If they're deemed "colour safe" (defined below), they can get Class 1 medical.
In your case, presumably, you were not deemed colour safe since you're daytime-only Class 2, if that's indeed the case, then unfortunately Class 1 will not be possible according to the EASA regulations below:
MED.B.075 Colour vision
(a) Applicants shall be assessed as unfit, where they cannot
demonstrate their ability to readily perceive the colours that are
necessary for the safe exercise of the privileges of the licence.
(b) Examination and assessment
Applicants shall be subjected to the Ishihara test for the initial issue of a medical certificate. Applicants who pass that test may be
assessed as fit.
For a class 1 medical certificate:
Applicants who do not pass the Ishihara test shall be referred to the medical assessor of the licensing authority and shall undergo
further colour perception testing to establish whether they are colour
Applicants shall be normal trichromats or shall be colour safe.
Applicants who fail further colour perception testing shall be assessed as unfit.
For a class 2 medical certificate:
Applicants who do not pass the Ishihara test shall undergo further colour perception testing to establish whether they are colour safe.
Applicants who do not have satisfactory perception of colours shall be limited to exercising the privileges of the applicable licence in
— Commission Regulation (EU) No 1178/2011
"Colour safe" from the same source means:
... the ability of an applicant to readily distinguish the colours used in air navigation and to correctly identify aviation coloured lights.