What is Prussian blue?
<!--{{colourswatch|Prussian blue|003153}}--> {{Distinguish|Persian blue}} {{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 464375726 | Name = | IUPACName = Iron(II,III) hexacyanoferrate(II,III) | SystematicName = <!-- Iron(3+) hexacyanoirontetrauide (substitutive) OR Iron(3+) hexacyanidoferrate(4-) (additive)--> | OtherNames = {{ubl|Berlin blue |Ferric ferrocyanide |Ferric hexacyanoferrate |Iron(III) ferrocyanide |Iron(III) hexacyanoferrate(II) |Parisian blue }} | Section1 = {{Chembox Identifiers | InChI = 1S/18CN.7Fe/c18*1-2;;;;;;;/q;;;;;;;;;;;;;;;;;;3*-4;4*+3 | InChIKey1 = DNMNDNSFJMUUFM-UHFFFAOYSA-N | CASNo = 14038-43-8 | CASNo_Ref = {{cascite|correct|CAS}} | PubChem = 2724251 | ChEMBL_Ref = {{ebicite|changed|EBI}} | ChEMBL = 2096629 | ChemSpiderID = 20074656 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | UNII = TLE294X33A | UNII_Ref = {{fdacite|correct|FDA}} | EINECS = 237-875-5 | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 30069 | Gmelin = 1093743 | SMILES = [Fe+3].[Fe+3].[Fe+3].[Fe+3].N#C[Fe-4](C#N)(C#N)(C#N)(C#N)C#N.N#C[Fe-4](C#N)(C#N)(C#N)(C#N)C#N.N#C[Fe-4](C#N)(C#N)(C#N)(C#N)C#N | StdInChI = 1S/18CN.7Fe/c18*1-2;;;;;;;/q;;;;;;;;;;;;;;;;;;3*-4;4*+3 | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = DNMNDNSFJMUUFM-UHFFFAOYSA-N | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} }} | Section2 = {{Chembox Properties | C=18 | Fe=7 | N=18 | Appearance = Blue opaque crystals}} | Section3 = | Section4 = | Section5 = | Section6 = {{Chembox Pharmacology | ATCCode_prefix = V03 | ATCCode_suffix = AB31 | AdminRoutes = Oral}} | Section7 = {{Chembox Hazards | ExternalSDS = [https://fscimage.fishersci.com/msds/62402.htm MSDS Prussian blue]}} | Section8 = {{Chembox Related | OtherCations = [[Potassium ferrocyanide]]<br /> [[Sodium ferrocyanide]]}} }} {{Infobox color| title= Prussian blue| hex= 003153| r=0|g=49|b=83| <!-- c=100|m=41|y=0|k=67| --> h=205 |s=100 |v=32 |source=[http://www.colorhexa.com/003153] |isccname=Dark blue}} '''Pr