A UV-Vis radiation curable security ink for producing a security feature exhibiting a blue color upon viewing in transmitted light and a metallic yellow color upon viewing in incident light, wherein said ink comprises: a) from 7.5 wt-% to 20 wt-% of silver nanoplatelets having a mean diameter in the range of 50 to 150 nm with a standard deviation of less than 60%, a mean thickness in the range of 5 to 30 nm with a standard deviation of less than 50%, and a mean aspect ratio higher than 2.0, wherein the mean diameter is determined by transmission electron microscopy and the mean thickness is determined by transmission electron microscopy, and wherein the silver nanoplatelets bear a surface stabilizing agent of general formula wherein the residue R A is a C 2 -C 4 alkyl group substituted with a hydroxy group; the residue R B is selected from a C 1 -C 4 alkyl group, and a C 2 -C 4 alkyl group substituted with a hydroxy group; and Cat + is an ammonium cation of general formula + NH 2 R C R D, wherein the residue R C is a C 2 -C 4 alkyl group substituted with a hydroxy group; and the residue R D is selected from a C 1 -C 4 alkyl group, and a C 2 -C 4 alkyl group substituted with a hydroxy group; b) from 45 wt-% to 80 wt-% of either a cycloaliphatic epoxide, or a mixture of a cycloaliphatic epoxide and one or more UV-Vis radiation curable compounds; c) one or more cationic photoinitiators; d) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of: hydroxyl, acrylate, methacrylate, and trialkoxysilyl; e) from 3 wt-% to 12 wt-% of a polyvinyl chloride copolymer containing at least 60 wt-% of vinyl chloride; and optionally f) up to 25 wt-% of an organic solvent; the weight percents being based on the total weight of the UV-Vis radiation curable security ink. a) from 7.5 wt-% to 20 wt-% of silver nanoplatelets having a mean diameter in the range of 50 to 150 nm with a standard deviation of less than 60%, a mean thickness in the range of 5 to 30 nm with a standard deviation of less than 50%, and a mean aspect ratio higher than 2.0, wherein the mean diameter is determined by transmission electron microscopy and the mean thickness is determined by transmission electron microscopy, and wherein the silver nanoplatelets bear a surface stabilizing agent of general formula wherein the residue R A is a C 2 -C 4 alkyl group substituted with a hydroxy group; the residue R B is selected from a C 1 -C 4 alkyl group, and a C 2 -C 4 alkyl group substituted with a hydroxy group; and Cat + is an ammonium cation of general formula + NH 2 R C R D, wherein the residue R C is a C 2 -C 4 alkyl group substituted with a hydroxy group; and the residue R D is selected from a C 1 -C 4 alkyl group, and a C 2 -C 4 alkyl group substituted with a hydroxy group; wherein the silver nanoplatelets bear a surface stabilizing agent of general formula wherein the residue R A is a C 2 -C 4 alkyl group substituted with a hydroxy group; the residue R B is selected from a C 1 -C 4 alkyl group, and a C 2 -C 4 alkyl group substituted with a hydroxy group; and Cat + is an ammonium cation of general formula + NH 2 R C R D, wherein the residue R C is a C 2 -C 4 alkyl group substituted with a hydroxy group; and the residue R D is selected from a C 1 -C 4 alkyl group, and a C 2 -C 4 alkyl group substituted with a hydroxy group; b) from 45 wt-% to 80 wt-% of either a cycloaliphatic epoxide, or a mixture of a cycloaliphatic epoxide and one or more UV-Vis radiation curable compounds; c) one or more cationic photoinitiators; d) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of: hydroxyl, acrylate, methacrylate, and trialkoxysilyl; e) from 3 wt-% to 12 wt-% of a polyvinyl chloride copolymer containing at least 60 wt-% of vinyl chloride; and optionally f) up to 25 wt-% of an organic solvent;